Co-reporter:A. Mohan Raj and V. Ramamurthy
Organic Letters November 17, 2017 Volume 19(Issue 22) pp:6116-6116
Publication Date(Web):October 30, 2017
DOI:10.1021/acs.orglett.7b02963
To probe the role of the supramolecular steric effects and free volume on photoreactions, geometric isomerization of neutral azobenzenes (ABs) and their radical ions, generated by electron transfer with gold nanoparticles, included within an octa acid capsule, was investigated. A comparison of the isomerization of ABs that proceed by volume conserving pyramidalization and stilbene analogues that proceed by volume demanding one bond flip has indicated the differing influence of 4-alkyl groups on these two processes.
Co-reporter:Mintu Porel, Nithyanandhan Jayaraj, Lakshmi S. Kaanumalle, Murthy V. S. N. Maddipatla, Anand Parthasarathy and V. Ramamurthy
Langmuir March 17, 2009 Volume 25(Issue 6) pp:3473-3481
Publication Date(Web):February 16, 2009
DOI:10.1021/la804194w
We have been exploring the use of a deep cavity cavitand known by the trivial name ‘octa acid’ as a photochemical reaction cavity for manipulating photochemical and photophysical properties of organic molecules. In the current study, we have monitored the micropolarity of the interior of the cavitand by recording the fluorescence of five different organic probes. They all indicate that the interior of octa acid capsuleplex (2:1, H/G complex) is nonpolar and does not contain water molecules in spite of the complex being present in water. The nature of the octa acid−probe complex in each case has been characterized by 1H NMR data to be a 2:1 capsuleplex. Photophysical and 1H NMR experiments were employed to probe the factors that control the structure of the complex, 2:2, 2:1, and 1:1. The data we have on hand suggest that the structure of the host/guest complex depends on the size and hydrophobicity of the guest molecule.
Co-reporter:Srijana Bhandari, Zilong Zheng, Buddhadev Maiti, Chi-Hung Chuang, Mintu Porel, Zhi-Qiang You, Vaidhyanathan Ramamurthy, Clemens Burda, John M. Herbert, and Barry D. Dunietz
The Journal of Physical Chemistry C July 20, 2017 Volume 121(Issue 28) pp:15481-15481
Publication Date(Web):June 22, 2017
DOI:10.1021/acs.jpcc.7b05522
Encapsulation of dye molecules is used as a means to achieve charge separation across different dielectric environments. We analyze the absorption and emission spectra of several coumarin molecules that are encapsulated within an octa-acid dimer forming a molecular capsule. The water-solvated capsule effect on the coumarin’s electronic structure and absorption spectra can be understood as due to an effective dielectric constant where the capsule partially shields electrostatically the dielectric solvent environment. Blue-shifted emission spectra are explained as resulting from a partial intermolecular charge transfer where the capsule is the acceptor, and which reduces the coumarin relaxation in the excited state.
Co-reporter:Vaidhyanathan Ramamurthy and Jayaraman Sivaguru
Chemical Reviews 2016 Volume 116(Issue 17) pp:9914-9993
Publication Date(Web):June 2, 2016
DOI:10.1021/acs.chemrev.6b00040
Photochemistry, bearing significant applications in natural and man-made events such as photosynthesis, vision, photolithography, photodynamic therapy, etc., is yet to become a common tool during the synthesis of small molecules in a laboratory. Among other rationale, the inability to influence photochemical reactions with temperature, solvent, additives, etc., dissuades chemists from employing light-initiated reactions as a routine synthetic tool. This review highlights how diverse, highly organized structures such as solvent-free crystals and water-soluble host–guest assemblies can be employed to control and manipulate photoreactions and thereby serve as an efficient tool for chemists, including those interested in synthesis. The efficacy of the media in modifying the excited-state behavior of organic molecules is illustrated with photocycloaddition in general and [2 + 2] photocycloaddition in particular, reactions widely employed in the synthesis of complex natural products as well as highly constrained molecules, as exemplars. The reaction media, highly pertinent in the context of green sustainable chemistry, include solvent-free crystals and solids such as silica, clay, and zeolite and water-soluble hosts that can solubilize and preorganize hydrophobic reactants in water. Since no other reagent would be more sustainable than light and no other medium greener than water, we believe that the supramolecular photochemistry expounded here has a momentous role as a synthetic tool in the future.
Co-reporter:Nareshbabu Kamatham, Débora C. Mendes, José P. Da Silva, Richard S. Givens, and V. Ramamurthy
Organic Letters 2016 Volume 18(Issue 21) pp:5480-5483
Publication Date(Web):October 18, 2016
DOI:10.1021/acs.orglett.6b02655
Photolysis of aqueous solutions of carboxylic acid esters of 7-(methoxycoumaryl)-4-methanol included within the capsule made up of two molecules of octaacid released the acids in water. The trigger 7-(methoxycoumaryl)-4-methyl chromophore remains within octaacid either as the alcohol or as an adduct with the host octaacid through a hydrogen abstraction process. The method established here offers a procedure to release hydrophobic acid molecules in water at will in a timely manner with light. In addition, the system offers an unanticipated opportunity to probe the mechanistic dichotomy of a diradicaloid intermediate expressing both radical and ionic behavior when generated by coumarylmethyl ester photolysis in a hydrophobic environment.
Co-reporter:A. Mohan Raj, Françisco M. Raymo, and V. Ramamurthy
Organic Letters 2016 Volume 18(Issue 7) pp:1566-1569
Publication Date(Web):March 21, 2016
DOI:10.1021/acs.orglett.6b00405
Octa acid (OA), a calixarene-based cavitand, forms a 1:2 capsular assembly with neutral 1,3,3-trimethyl-6′-nitrospiro[2H-1]benzopyran-2,2′-indoline and 1:1 cavitandplex with its open zwitterionic merocyanine form. Photochromic interconversion between the spiropyran and merocyanine leads to unprecedented reversible capsular disassembly and assembly. OA provides stability to the merocyanine in both the ground and excited states. The photochemically controlled disassembly and assembly process established here points toward the opportunity of using the OA capsule in delivering small molecules at the desired locations.
Co-reporter:Takuya Fujimura, Elamparuthi Ramasamy, Yohei Ishida, Tetsuya Shimada, Shinsuke Takagi and Vaidhyanathan Ramamurthy
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 7) pp:5404-5411
Publication Date(Web):12 Jan 2016
DOI:10.1039/C5CP06984J
To achieve the goal of energy transfer and subsequent electron transfer across three molecules, a phenomenon often utilized in artificial light harvesting systems, we have assembled a light absorber (that also serves as an energy donor), an energy acceptor (that also serves as an electron donor) and an electron acceptor on the surface of an anionic clay nanosheet. Since neutral organic molecules have no tendency to adsorb onto the anionic surface of clay, a positively charged water-soluble organic capsule was used to hold neutral light absorbers on the above surface. A three-component assembly was prepared by the co-adsorption of a cationic bipyridinium derivative, cationic zinc porphyrin and cationic octaamine encapsulated 2-acetylanthracene on an exfoliated anionic clay surface in water. Energy and electron transfer phenomena were monitored by steady state fluorescence and picosecond time resolved fluorescence decay. The excitation of 2-acetylanthracene in the three-component system resulted in energy transfer from 2-acetylanthracene to zinc porphyrin with 71% efficiency. Very little loss due to electron transfer from 2-acetylanthracene in the cavitand to the bipyridinium derivative was noticed. Energy transfer was followed by electron transfer from the zinc porphyrin to the cationic bipyridinium derivative with 81% efficiency. Analyses of fluorescence decay profiles confirmed the occurrence of energy transfer and subsequent electron transfer. Merging the concepts of supramolecular chemistry and surface chemistry we realized sequential energy and electron transfer between three hydrophobic molecules in water. Exfoliated transparent saponite clay served as a matrix to align the three photoactive molecules at a close distance in aqueous solutions.
Co-reporter:Giri Babu Veerakanellore, Burjor Captain and V. Ramamurthy
CrystEngComm 2016 vol. 18(Issue 25) pp:4708-4712
Publication Date(Web):11 May 2016
DOI:10.1039/C6CE00682E
With three examples, we have established that cis-cinnamic acids can dimerize via a diradical intermediate in the crystalline state provided that the intermolecular distance is less than 4.2 Å. In the excited state of cis-isomers, C–C bond formation with an adjacent molecule competes with geometric isomerization.
Co-reporter:Barnali Mondal, Burjor Captain, V. Ramamurthy
Journal of Photochemistry and Photobiology A: Chemistry 2016 Volume 331() pp:224-232
Publication Date(Web):1 December 2016
DOI:10.1016/j.jphotochem.2015.07.017
Cis-trans isomerization is one of the most common and well-investigated photoreaction of olefins in solution. This occurs via 180° rotation of one of the substituents on CC bond requiring large space around the double bond. One would expect that in crystals the neighboring molecules would prohibit such a process. In spite of this in early 1960s Schmidt and co-workers reported occurrence of such a process in crystals via 2 + 2 ‘meta cyclobutane’ formation. In this study by examining the photochemistry of four cis-stilbazolium salts we show that the photoconversion to the corresponding trans isomers does not occur via 2 + 2 addition. Large separation that ensures considerable space between neighboring olefins favors cis-trans isomerization in crystals. An aspect that is puzzling is that the product trans isomer phase separates and recrystallizes within the parent cis crystals and photodimerizes to the cyclobutane dimer. Details of this phenomenon are to be understood.•Cis to trans isomerization of stilbazolium salts occurs in crystalline state.•Metastable intermediate is not involved in the photoisomerization process.•Free space around the rotating group is essential.•The final product cyclobutane is not involved in the isomerization process.
Co-reporter:Takamasa Tsukamoto, Elamparuthi Ramasamy, Tetsuya Shimada, Shinsuke Takagi, and V. Ramamurthy
Langmuir 2016 Volume 32(Issue 12) pp:2920-2927
Publication Date(Web):March 10, 2016
DOI:10.1021/acs.langmuir.5b03962
Three coumarin derivatives (7-propoxy coumarin, coumarin-480, and coumarin-540a, 2, 3, and 4, respectively) having different absorption and emission spectra were encapsulated within a water-soluble organic capsule formed by the two positively charged ammonium-functionalized cavitand octaamine (OAm, 1). Guests 2, 3, and 4 absorb in ultraviolet, violet, and blue regions and emit in violet, blue, and green regions, respectively. Energy transfer between the above three coumarin@(OAm)2 complexes assembled on the surface of a saponite clay nanosheet was investigated by steady-state and time-resolved emission techniques. Judging from their emission and excitation spectra, we concluded that the singlet–singlet energy transfer proceeded from 2 to 3, from 2 to 4, and from 3 to 4 when OAm-encapsulated 2, 3, and 4 were aligned on a clay surface as two-component systems. Under such conditions, the energy transfer efficiencies for the paths 2* to 3, 2* to 4, and 3* to 4 were calculated to be 33, 36, and 50% in two-component systems. When all three coumarins were assembled on the surface and 2 was excited, the energy transfer efficiencies for the paths 2* to 3, 2* to 4, and 3* to 4 were estimated to be 32, 34, and 33%. A comparison of energy transfer efficiencies of the two-component and three-component systems revealed that excitation of 2 leads to emission from 4. Successful merging of supramolecular chemistry and surface chemistry by demonstrating novel multi-step energy transfer in a three-component dye encapsulated system on a clay surface opens up newer opportunities for exploring such systems in an artificial light-harvesting phenomenon.
Co-reporter:Anand Parthasarathy, V. Ramamurthy
Journal of Photochemistry and Photobiology A: Chemistry 2016 Volume 317() pp:132-139
Publication Date(Web):15 February 2016
DOI:10.1016/j.jphotochem.2015.11.005
•Selective photodimerization of indene in the aqueous medium was achieved by encapsulation of indene within a self-assembled cavitand capsule.•The major product (photodimer) formed within capsular complex is uncommon in organic solvents by both direct excitation and sensitization approaches.In the context of green chemistry, identifying strategies to carry out organic reactions in aqueous medium in the absence of organic and inorganic reagents is important. We show below that octa acid (OA), a water-soluble cavitand, is capable of solubilizing water insoluble reactant in water and yielding selective product by confining the reactants and intermediates during a light initiated reaction. By employing indene as the substrate we have observed that the OA capsule upon irradiation facilitates the formation of anti-head–tail dimer, the isomer that is generally not obtained upon direct excitation and triplet and electron transfer sensitizations in isotropic organic solvents.
Co-reporter:Yashapal Singh, A. Mohan Raj, B.M. Kiran, J. Nithyanandhan, V. Ramamurthy, N. Jayaraman
Journal of Photochemistry and Photobiology A: Chemistry 2016 Volume 317() pp:125-131
Publication Date(Web):15 February 2016
DOI:10.1016/j.jphotochem.2015.10.020
•Dendrimer as the water-soluble host molecule.•Non-covalent dyes encapsulation in aqueous dendrimer medium.•Steady-state and time-resolved measurements of dyes in dendrimer host.•FRET processes of dye molecules inside dendrimer host.•Expanding the visible light absorption and emission wavelengths.A water soluble third generation poly(alkyl aryl ether) dendrimer was examined for its ability to solubilize hydrophobic polyaromatic molecules in water and facilitate non-radiative resonance energy transfer between them. One to two orders of magnitude higher aqueous solubilities of pyrene (PY), perylene (PE), acridine yellow (AY) and acridine orange (AO) were observed in presence of a defined concentration of the dendrimer. A reduction in the quantum yield of the donor PY* emission and a partial decrease in lifetime of the donor excited state revealed the occurrence of energy transfer from dendrimer solubilized excited PY to ground state PE molecules, both present within a dendrimer. The energy transfer efficiency was estimated to be ∼61%. A cascade resonance energy transfer in a three component system, PY*-to-PE-to-AY and PY*-to-PE-to-AO, was demonstrated through incorporation of AY or AO in the two-component PY–PE system. In the three-component system, excitation of PY resulted in emission from AY or AO via a cascade energy transfer process. Careful choice of dye molecules with good spectral overlap and the employment of dendrimer as the medium enabled us to expand absorption-emission wavelengths, from ∼330 nm to ∼600 nm in aqueous solution.
Co-reporter:J. Shailaja, J. Sivaguru, V. Ramamurthy
Journal of Photochemistry and Photobiology A: Chemistry 2016 Volume 331() pp:197-205
Publication Date(Web):1 December 2016
DOI:10.1016/j.jphotochem.2016.02.010
•Zeolite that encapsulates 1O2 sensitizers promotes selective photooxidation.•Short irradiation time results in selective oxidation of olefins.•Zeolites with light cations favor 1O2 generation via energy transfer.•Zeolites with heavy cations lead to dye decomposition via electron transfer.Thiazine dyes such as thionine, methylene blue and methylene green were exchanged within monovalent cation exchanged Y zeolites. Depending on the water content the dye molecules exist as either monomer (‘dry’) or dimer (‘wet’). The monomeric dye is effective in producing singlet oxygen by energy transfer process inside the zeolite cavity. In polar zeolites like LiY, NaY energy transfer predominates whereas in basic zeolites like CsY electron transfer overtakes the energy transfer leading to the photo-destruction of the dye. While on short time of irradiation, energy transfer to oxygen led to selectivity in the product distribution, but on prolonged irradiation, destruction of the dye through electron transfer was the main outcome.
Co-reporter:V. Ramamurthy and Shipra Gupta
Chemical Society Reviews 2015 vol. 44(Issue 1) pp:119-135
Publication Date(Web):15 Oct 2014
DOI:10.1039/C4CS00284A
Photochemical and photophysical behavior of molecules in supramolecular assemblies are different and more selective than in gas and isotropic solution phases. Knowledge of the inherent electronic and steric properties of the reactant is insufficient to predict the excited state behavior of molecules confined in such assemblies. Weak interactions between the medium and the reactant as well as the free space in a reaction cavity would play a significant role in modulating the excited state properties of molecules when they are included within confined spaces. The concepts of ‘Molecular Photochemistry’ should be modified while applying them to ‘Supramolecular Photochemistry’. In this review we show that the topochemical rules established to understand reactions in crystals could be extended to supramolecular assemblies in general. To make the best use of the medium one needs to understand the features of the medium, the nature of interaction between the medium and the molecule and the rules that govern the behavior of a molecule in that medium. This tutorial provides introduction to these aspects of ‘Supramolecular Photochemistry’.
Co-reporter:Pradeepkumar Jagadesan, José P. Da Silva, Richard S. Givens, and V. Ramamurthy
Organic Letters 2015 Volume 17(Issue 5) pp:1276-1279
Publication Date(Web):February 23, 2015
DOI:10.1021/acs.orglett.5b00252
We report the clean, efficient photorelease of a series of carboxylic acids embedded in octa acid (OA) host and protected by a p-hydroxyphenacyl cage. A key role is played by the cage by providing hydrophobicity for entry into the OA enclosure and yet readily removable as a photoactivated protecting group for release from the host. The rapid photo-Favorskii rearrangement of the departing chromophore does not react with the host OA but diminishes hydrophobicity of the OA contents, leading to their facile release into the solvent.
Co-reporter:Balakrishna R. Bhogala;Burjor Captain
Photochemistry and Photobiology 2015 Volume 91( Issue 3) pp:696-704
Publication Date(Web):
DOI:10.1111/php.12353
Abstract
Photodimerization of cocrystals of four bispyridylethylenes and two stilbazoles with urea as a template in the solid state has been investigated following our success with thiourea. Four investigated olefins photodimerized quantitatively to a single dimer in the crystalline state only. The reactivity of urea–olefin crystals is understood on the basis of their packing arrangements in the crystalline state. In reactive crystals the adjacent reactive molecules are within 4.2 Å and parallel, whereas the unreactive ones have their adjacent molecules are farther than 4.6Å and nonparallel. Thus, with the knowledge of crystal packing the reactivity of urea–olefin crystals is predictable on the basis of Schmidt's topochemical postulates. The templating property of urea, similar to thiourea, derives from its ability to form hydrogen bonds with itself and the guest olefins. Despite the similarities in molecular structures of urea and thiourea their subtle electronic properties, yet to be fully understood, affect the crystal packing and consequently their reactivity in the crystalline state. Further work is needed to fully exploit the templating properties of urea.
Co-reporter:V. Ramamurthy, Steffen Jockusch, and Mintu Porel
Langmuir 2015 Volume 31(Issue 20) pp:5554-5570
Publication Date(Web):December 2, 2014
DOI:10.1021/la504130f
Supramolecular assemblies that help to preorganize reactant molecules have played an important role in the development of concepts related to the control of excited-state processes. This has led to a persistent search for newer supramolecular systems (hosts), and this review briefly presents our work with octa acid (OA) to a host to control excited-state processes of organic molecules. Octa acid, a water-soluble host, forms 1:1, 2:1, and 2:2 (host–guest) complexes with various organic molecules. A majority of the guest molecules are enclosed within a capsule made up of two molecules of OA whereas OA by itself remains as a monomer or aggregates. Luminescence and 1H NMR spectroscopy help to characterize the structure and dynamics of these host–guest complexes. The guest molecule as well as the host–guest complex as a whole undergoes various types of motion, suggesting that the guests possess freedom inside the confined space of the octa acid capsule. In addition, the confined guests are not isolated but are able to communicate (energy, electron, and spin) with molecules present closer to the capsule. The host–guest complexes are stable even on solid surfaces such as silica, clay, α-Zr phosphate, TiO2, and gold nanoparticles. This opens up new opportunities to explore the interaction between confined guests and active surfaces of TiO2 and gold nanoparticles. In addition, this allows the possibility of performing energy and electron transfer between organic molecules that do not adsorb on inert surfaces of silica, clay, or α-Zr phosphate. The results summarized here, in addition to providing a fundamental understanding of the behavior of molecules in a confined space provided by the host OA, are likely to have a long-range effect on the capture and release of solar energy.
Co-reporter:V. Ramamurthy, Barnali Mondal
Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2015 Volume 23() pp:68-102
Publication Date(Web):June 2015
DOI:10.1016/j.jphotochemrev.2015.04.002
•Supramolecular photochemistry relates to the behavior of confined molecules.•Supramolecular photochemistry is understood in terms of reaction cavity concept.•Appropriate molecular container should be chosen to achieve the desired goal.‘Supramolecular photochemistry’ (SP) deals with a study of the properties of molecules in their excited states where the medium plays a significant role. While ‘molecular photochemistry’ (MP) deals with studies in isotropic solution, the SP deals with reactant molecules that interact weakly with their surroundings. The surroundings in general are highly organized assemblies such as crystals, liquid crystals, micelles, and host–guest structures. The behavior of exited molecules in SP unlike in isotropic solution is controlled not only by their inherent electronic and steric properties but also by the immediate surroundings. The weak interactions that control the chemistry include van der Walls, hydrophobic, CH⋯π, π⋯π and several types of hydrogen bonds. In this review the uniqueness of SP compared to MP is highlighted with examples chosen from reactions in crystals, micelles and host–guest assemblies. In spite of distinctly different structures (crystals, micelles, etc.) the influence of the medium could be understood on the basis of a model developed by G.M.J. Schmidt for photoreactions in crystals. The principles of reaction cavity model are briefly outlined in this review. There are a few important features that are specific to SP. For example, highly reactive molecules and intermediates could be stabilized in a confined environment; they enable phosphorescence to be observed at room temperature and favor chiral induction in photochemical reactions. Using such examples the uniqueness of SP is highlighted. The future of SP depends on developing efficient and unique catalytic photoreactions using easily available reaction ‘containers’. In addition, their value in artificial photosynthesis should be established for SP to occupy a center stage in the future.
Co-reporter:Shampa R. Samanta, José P. Da Silva, Anthony Baldridge, Laren M. Tolbert, and V. Ramamurthy
Organic Letters 2014 Volume 16(Issue 12) pp:3304-3307
Publication Date(Web):May 30, 2014
DOI:10.1021/ol5013058
Excited state behavior of halogen substituted model GFP chromophores was investigated in an acetonitrile solution and in a confined environment provided by an octa acid capsule in water. Of the ortho, meta, and para halogen substituted GFP chromophores only the ortho compounds gave a new product resulting from an unprecedented photosubstitution of halogens by the hydroxyl group. This unusual reaction highlights the importance of confined spaces in bringing about some unattainable photoreactions.
Co-reporter:Barnali Mondal, Tingting Zhang, Rajeev Prabhakar, Burjor Captain and V. Ramamurthy
Photochemical & Photobiological Sciences 2014 vol. 13(Issue 11) pp:1509-1520
Publication Date(Web):23 Jul 2014
DOI:10.1039/C4PP00221K
A difference in photobehavior and molecular packing between hydrated and anhydrous crystals of protonated trans-stilbazoles has been identified. While stilbazoles are not photoreactive in the crystalline state, upon protonation with HCl in the solid state they dimerized to a single dimer (anti-head–tail) when exposed to UV light. In these photoreactive crystals the protonated stilbazole molecules are arranged in a ladder-like format with the rungs made up of water molecules and chloride ions. A combination of water and chloride ion holds the protonated trans-stilbazoles through either N–H⋯O or N–H⋯Cl− interactions. Anhydrous protonated stilbazole crystals prepared by heating the ‘wet’ crystals under reduced pressure were inert upon exposure to UV light. As per X-ray crystal structure analyses these light stable crystals did not contain water molecules in their lattice. The current investigation has established that water molecules are essential for photodimerization of crystalline protonated trans-stilbazoles. To compare the reactivity of protonated trans-stilbazoles with that of protonated cis-stilbazoles, photoreactivity and packing arrangement of cis-4-iodo stilbazole·HCl salt was examined. This molecule in the crystalline state only isomerized to the trans isomer and did not dimerize. Thus, while the trans isomer dimerized and did not isomerize, the cis isomer only isomerized and did not dimerize in the crystalline state. To probe the role of cation⋯π interaction in the packing of protonated trans-stilbazoles, energies of various types of packing in the gas phase were estimated by MP-2 calculations and cation⋯π interaction was found to be unimportant in the packing of protonated trans-stilbazole crystals investigated here.
Co-reporter:Yohei Ishida ; Revathy Kulasekharan ; Tetsuya Shimada ; V. Ramamurthy ;Shinsuke Takagi
The Journal of Physical Chemistry C 2014 Volume 118(Issue 19) pp:10198-10203
Publication Date(Web):April 17, 2014
DOI:10.1021/jp502816j
We report the occurrence of efficient energy transfer reaction in a novel host–guest assembly composed of an anionic clay nanosheet, cationic porphyrin, and neutral aromatic molecule encapsulated within a cationic organic cavitand. The supramolecular assembly was prepared by the coadsorption of tetracationic Zn–porphyrin (acceptor) and 2-acetylanthracene (donor) enclosed within cationic organic cavitand (octaamine in its protonated form) on anionic clay nanosheets. In this arrangement under the interguest distance of 2.4 nm, almost 100% efficiency of singlet–singlet energy transfer was achieved. Detailed time-resolved fluorescence measurements revealed that the energy transfer rate constant could be attributed to a single component (1.9 × 109 s–1). This strongly suggests that the adsorption distribution of porphyrin and cavitand is rather uniform, not segregated. This is a progress from our previous study that involves energy transfer between two encapsulated neutral molecules. The use of Zn–porphyrin as an energy acceptor in this study enables to connect this energy transfer system to charge separation processes in the same manner as natural photosynthetic systems do; moreover, the efficiency of energy transfer reaction improved to almost 100% from 85% in the previous system between two cavitands.
Co-reporter:Shampa R. Samanta, Rajib Choudhury, and V. Ramamurthy
The Journal of Physical Chemistry A 2014 Volume 118(Issue 45) pp:10554-10562
Publication Date(Web):July 28, 2014
DOI:10.1021/jp505196v
Geometric isomerization of light-activated olefins plays a significant role in biological events as well as in modern materials science applications. In these systems, the isomerization occurs in highly confined spaces, and concepts derived from solution investigations are only partially applicable. This study makes contributions in understanding the excited-state behavior of olefins in confined spaces by investigating the excited-state behavior of 1,4-diphneyl-13-butadiene (DPB) and 1,4-ditolyl-1,3-butadiene (DTB) encapsulated in a well-defined organic capsule made up of the octa acid (OA) host. Both of these dienes that exist in three isomeric forms (trans,trans; trans,cis; and cis,cis) formed 1:2 guest–host complexes with OA in aqueous borate buffer. Competition experiments monitored by 1H NMR signals revealed that among the three isomers the cis,cis isomer of DPB and DTB formed the most stable complex with OA. Molecular modeling studies suggested that all six isomers of DPB and DTB preferred the cisoid conformation within the OA capsule. Irradiation (>280 nm) of the diene–OA complex (diene@OA2) resulted in geometric isomerization, and the photostationary state consisted of cis,trans isomer as major and cis,cis as minor products. The photostationary state could be enriched with the cis,cis isomer in yields close to 70% with proper cutoff filters because the cis,cis isomer absorbs at shorter wavelength than the other two isomers. Consistent with the MD simulation prediction that trans,trans-DPB and trans,trans-DTB existed in cisoid conformation within OA capsule, the generation of singlet oxygen in the presence of OA encapsulated DPB or DTB resulted in facile [4 + 2] addition between the diene and the singlet oxygen.
Co-reporter:Nithyanandhan Jayaraj, Pradeepkumar Jagadesan, Shampa R. Samanta, José P. Da Silva, and V. Ramamurthy
Organic Letters 2013 Volume 15(Issue 17) pp:4374-4377
Publication Date(Web):August 27, 2013
DOI:10.1021/ol4019024
Examples of release of organic acids from encapsulated p-methoxyphenacyl esters provided here demonstrate the value of a phototrigger strategy to release chemicals of interest in water from hydrophobic precursors. In this study, a photochemical β-cleavage process centered on the p-methoxyphenacyl group is exploited to release the acid of interest from a water-soluble capsule made up of octa acid.
Co-reporter:Pradeepkumar Jagadesan, Barnali Mondal, Anand Parthasarathy, V. Jayathirtha Rao, and V. Ramamurthy
Organic Letters 2013 Volume 15(Issue 6) pp:1326-1329
Publication Date(Web):March 1, 2013
DOI:10.1021/ol400267k
Two deep cavity cavitands, octa acid and resorcinol-capped octa acid, have been established to be good triplet energy donors in the excited state and electron donors in the ground state to excited acceptors. This property endows them the capacity to be “active” reaction containers. The above recognition provides opportunities to investigate the excited state chemistry of host-encapsulated guests without the use of secondary triplet energy and electron donors.
Co-reporter:Mintu Porel, M. Francesca Ottaviani, Steffen Jockusch, Nicholas J. Turro and V. Ramamurthy
RSC Advances 2013 vol. 3(Issue 2) pp:427-431
Publication Date(Web):20 Nov 2012
DOI:10.1039/C2RA22285J
Supramolecular interactions of polynitroxides with γ-cyclodextrin (γ-CD) were used to control intramolecular electron spin–spin exchange couplings in these stable radicals. In the absence of γ-CD, the binitroxide T2 and trinitroxide T3 showed strong spin–spin coupling as evidenced by the high exchange coupling constant of J = 120 MHz for T2 in its EPR spectra. Host/guest complexes are formed upon addition of γ-CD to the polynitroxides where the nitroxide moiety interacts with the γ-CD cavity, which causes suppression of spin exchange. By variation of the host/guest ratio, the nature of a trinitroxide spin system can be tuned from a three-spin to a two-spin to a one-spin system. In addition to the host/guest ratio, the spin exchange coupling can also be tuned by temperature, which shifts the equilibrium between CD-encapsulated nitroxides and free nitroxides.
Co-reporter:Rajib Choudhury, Arghya Barman, Rajeev Prabhakar, and V. Ramamurthy
The Journal of Physical Chemistry B 2013 Volume 117(Issue 1) pp:398-407
Publication Date(Web):December 6, 2012
DOI:10.1021/jp3090815
In this study we have examined the conformational preference of phenyl-substituted hydrocarbons (alkanes, alkenes, and alkynes) of different chain lengths included within a confined space provided by a molecular capsule made of two host cavitands known by the trivial name “octa acid” (OA). One- and two-dimensional 1H NMR experiments and molecular dynamics (MD) simulations were employed to probe the location and conformation of hydrocarbons within the OA capsule. In general, small hydrocarbons adopted a linear conformation while longer ones preferred a folded conformation. In addition, the extent of folding and the location of the end groups (methyl and phenyl) were dependent on the group (H2C–CH2, HC═CH, and C≡C) adjacent to the phenyl group. In addition, the rotational mobility of the hydrocarbons within the capsule varied; for example, while phenylated alkanes tumbled freely, phenylated alkenes and alkynes resisted such a motion at room temperature. Combined NMR and MD simulation studies have confirmed that molecules could adopt conformations within confined spaces different from that in solution, opening opportunities to modulate chemical behavior of guest molecules.
Co-reporter:Rajib Choudhury, Shipra Gupta, José P. Da Silva, and V. Ramamurthy
The Journal of Organic Chemistry 2013 Volume 78(Issue 5) pp:1824-1832
Publication Date(Web):August 29, 2012
DOI:10.1021/jo301499t
1-azidoadamantane and 2-azidoadamantane form a 1:1 complex with hosts octa acid (OA) and cucurbit[7]uril (CB7) in water. Isothermal titration calorimetric measurements suggest these complexes to be very stable in aqueous solution. The complexes have been characterized by 1H NMR in solution and by ESI-MS in gas phase. In both phases, the complexes are stable. Irradiation of these complexes (λ > 280 nm) results in nitrenes via the loss of nitrogen from the guest azidoadamantanes. The behavior of nitrenes within OA differs from that in solution. Nitrenes included within octa acid attack one of the four tertiary benzylic hydrogens present at the lower interior part of OA. While in solution intramolecular insertion is preferred, within OA intermolecular C–H insertion seems to be the choice. When azidoadamantanes included in CB7 were irradiated (λ > 280 nm) the same products as in solution resulted but the host held them tightly. Displacement of the product required the use of a higher binding guest. In this case, no intermolecular C–H insertion occurred. Difference in reactivity between OA and CB7 is the result of the location of hydrogens; in OA they are in the interior of the cavity where the nitrene is generated, and in CB7 they are at the exterior. Reactivity of nitrenes within OA is different from that of carbenes that do not react with the host.
Co-reporter:Revathy Kulasekharan, Murthy V. S. N. Maddipatla, Anand Parthasarathy, and V. Ramamurthy
The Journal of Organic Chemistry 2013 Volume 78(Issue 3) pp:942-949
Publication Date(Web):December 29, 2012
DOI:10.1021/jo3023928
Optically pure α-alkyl deoxybenzoins resulting in products of Norrish Type I and Type II reactions upon excitation has been investigated within the octa acid (OA) capsule in water. The product distribution was different from that in an organic solvent and was also dependent on the length of the α-alkyl chain. Most importantly, a rearrangement product not formed in an organic solvent arising from the triplet radical pair generated by Norrish Type I reaction was formed, and its yield was dependent on the alkyl chain length. In an organic solvent, since the cage lifetime is shorter than the time required for intersystem crossing (ISC) of the triplet radical pair to the singlet radical pair the recombination with or without rearrangement of the primary radical pair (phenylacetyl and benzyl) does not occur. Recombination without rearrangement within the capsule as inferred from monitoring the racemization of the optically pure α-alkyl deoxybenzoins suggesting the capsule’s stability for at least 10–8 s (the time required for ISC) is consistent with our previous photophysical studies that showed partial opening and closing of the capsule in the time range of microseconds.
Co-reporter:Barnali Mondal, Nareshbabu Kamatham, Shampa R. Samanta, Pradeepkumar Jagadesan, Jibao He, and V. Ramamurthy
Langmuir 2013 Volume 29(Issue 41) pp:12703-12709
Publication Date(Web):September 23, 2013
DOI:10.1021/la403310e
Water-soluble gold nanoparticles (AuNP) stabilized with cavitands having carboxylic acid groups have been synthesized and characterized by a variety of techniques. Apparently, the COOH groups similar to thiol are able to prevent aggregation of AuNP. These AuNP were stable either as solids or in aqueous solution. Most importantly, these cavitand functionalized AuNP were able to include organic guest molecules in their cavities in aqueous solution. Just like free cavitands (e.g., octa acid), cavitand functionalized AuNP includes guests such as 4,4′-dimethylbenzil and coumarin-1 through capsule formation. The exact structure of the capsular assembly is not known at this stage. Upon excitation there is communication between the excited guest present in the capsule and gold atoms and this results in quenching of phosphorescence from 4,4′-dimethylbenzil and fluorescence from coumarin-1.
Co-reporter:Yohei Ishida, Revathy Kulasekharan, Tetsuya Shimada, Shinsuke Takagi, and V. Ramamurthy
Langmuir 2013 Volume 29(Issue 6) pp:1748-1753
Publication Date(Web):January 29, 2013
DOI:10.1021/la305148j
A supramolecular host–guest assembly composed of a cationic organic cavitand (host), neutral aromatic molecules (guests), and an anionic clay nanosheet has been prepared and demonstrated that in this arrangement efficient singlet–singlet energy transfer could take place. The novelty of this system is the use of a cationic organic cavitand that enabled neutral organic molecules to be placed on an anionic saponite nanosheet. Efficient singlet–singlet energy transfer between neutral pyrene and 2-acetylanthracene enclosed within a cationic organic cavitand (octa amine) arranged on a saponite nanosheet was demonstrated through steady-state and time-resolved emission studies. The high efficiency was realized from the suppression of aggregation, segregation, and self-fluorescence quenching. We believe that the studies presented here using a novel supramolecular assembly have expanded the types of molecules that could serve as candidates for efficient energy-transfer systems, such as in an artificial light-harvesting system.
Co-reporter:Anand Parthasarathy;Shampa R. Samanta;V. Ramamurthy
Research on Chemical Intermediates 2013 Volume 39( Issue 1) pp:73-87
Publication Date(Web):2013 January
DOI:10.1007/s11164-012-0633-7
Conducting reactions in environmentally benign conditions is one of the major objectives of “green chemistry.” In this context, developing ways to conduct reactions in water seems obvious. In this report, we present our results on photodimerization of select guest molecules placed within the rigid reaction cavity of a water-soluble cavitand, octa acid. The results presented herein highlight the value of a supramolecular approach in achieving selectivity in photoreactions and opening reaction pathways that are latent in solution chemistry.
Co-reporter:Mintu Porel ; Chi-Hung Chuang ; Clemens Burda
Journal of the American Chemical Society 2012 Volume 134(Issue 36) pp:14718-14721
Publication Date(Web):August 29, 2012
DOI:10.1021/ja3067594
Supramolecular photoinduced electron transfer dynamics between coumarin 153 (C153) and 4,4′-dimethyl viologen dichloride (MV2+) across the molecular barrier of a host molecule, octa acid (OA), has been investigated with femtosecond time resolution. The ultrafast electron transfer from C153 to MV2+ followed excitation with 150 fs laser pulses at a wavelength of 390 nm despite the fact that C153 was incarcerated within an OA2 capsule. As a result, the photoexcited coumarin did not show any of the typical relaxation dynamics that is usually observed in free solution. Instead, the excited electron was transferred across the molecular wall of the capsuleplex within 20 ps. Likewise, the lifetime of the charge transfer state was short (724 ps), and electron back-transfer reestablished the ground state of the system within 1 ns, showing strong electronic coupling among the excited electron donor, host, and acceptor. When the donor was encapsulated into the host molecule, the electron transfer process showed significantly accelerated dynamics and essentially no solvent relaxation compared with that in free solution. The study was also extended to N-methylpyridinium iodide as the acceptor with similar results.
Co-reporter:José P. Da Silva, Revathy Kulasekharan, Carlos Cordeiro, Steffen Jockusch, Nicholas J. Turro, and V. Ramamurthy
Organic Letters 2012 Volume 14(Issue 2) pp:560-563
Publication Date(Web):December 23, 2011
DOI:10.1021/ol203139v
Nanocapsules, made up of the deep cavitand octa amine and several guests, were prepared in aqueous acidic solution and were found to be stable in the gas phase as detected by electrospray ionization mass spectrometry (ESI-MS). The observed gas phase host–guest complexes contained five positive charges and were associated with several acid molecules (HCl or HBr).
Co-reporter:S. R. Samanta, A. Parthasarathy and V. Ramamurthy
Photochemical & Photobiological Sciences 2012 vol. 11(Issue 11) pp:1652-1660
Publication Date(Web):24 May 2012
DOI:10.1039/C2PP25115A
Triplet sensitized photoisomerization of several stilbenes included within a water-soluble organic capsule has been investigated. In this study octa acid that self assembles in the presence of hydrophobic guest molecules to form a host–guest complex is utilized to solubilize hydrophobic stilbenes and triplet sensitizers in water, and to provide confinement during the geometric isomerization of included olefins. By monitoring the steady state and time resolved room temperature phosphorescence from 4,4′-dimethylbenzil in the presence of acceptor stilbenes and their nitrogen analogues (stilbazole and bispyridyl ethylene) we have been able to establish that triplet-triplet energy transfer occurs between encapsulated donors and encapsulated (or free) acceptors. The mechanism of the energy transfer process is yet to be fully understood although a similar phenomenon has been reported earlier in the literature with Cram's hemicarcerand as the host. The photostationary state composition of cis and trans isomers within the OA capsule is dependent on the relative binding strength of the two isomers with the OA capsule. Further investigation is needed to fully exploit the interesting observations made here to steer the photoisomerization towards a single isomer.
Co-reporter:Mintu Porel, Agnieszka Klimczak, Marina Freitag, Elena Galoppini, and V. Ramamurthy
Langmuir 2012 Volume 28(Issue 7) pp:3355-3359
Publication Date(Web):February 3, 2012
DOI:10.1021/la300053r
Coumarins C-153, C-480, and C-1 formed 1:2 (guest:host) complexes with a water-soluble cavitand having eight carboxylic acid groups (OA) in aqueous borate buffer solution. The complexes were photoexcited in the presence of electron acceptors (methyl viologen, MV2+, or TiO2) to probe the possibility of electron transfer between a donor and an acceptor physically separated by a molecular wall. In solution at basic pH, the dication MV2+ was associated to the exterior of the complex C-153@OA2, as suggested by diffusion constants (∼1.2 × 10–6 cm2/s) determined by DOSY NMR. The fluorescence of C-153@OA2 was quenched in the presence of increasing amounts of MV2+ and Stern–Volmer plots of Io/I and τo/τ vs [MV2+] indicated that the quenching was static. As per FT-IR-ATR spectra, the capsule C-153@OA2 was bound to TiO2 nanoparticle films. Selective excitation (λexc = 420) of the above bound complex resulted in fluorescence quenching. When adsorbed on insulating ZrO2 nanoparticle films, excitation of the complex resulted in a broad fluorescence spectrum centered at 500 nm and consistent with C-153 being within the lipophilic capsule interior. Consistent with the above results, colloidal TiO2 quenched the emission while colloidal ZrO2 did not.
Co-reporter:Shipra Gupta, Rajib Choudhury, Daniel Krois, Udo H. Brinker, and V. Ramamurthy
The Journal of Organic Chemistry 2012 Volume 77(Issue 11) pp:5155-5160
Publication Date(Web):May 15, 2012
DOI:10.1021/jo300571p
Adamantanediazirines, precursors of adamantanylidenes, form 1:1 complexes (guest to host) with cucurbit[7]uril and cucurbit[8]uril and a 3:1 complex with a Pd nanocage in water. 1H NMR spectra suggested that these complexes are stable in water on the NMR time scale. While photolysis of adamantanediazirines in water gave mainly adamantanone and adamantanol via adamantanylidene as intermediate, the 1:1 complexes of adamantanediazirine with cucurbiturils gave intramolecular C–H insertion products of adamantanylidene in >90% yield. The study establishes that significant control of carbene reactivity can be achieved when the precursor is encapsulated within a tight inert cavity. While the general characteristics of molecular containers can be understood on the basis of concepts such as “confinement” and “weak interactions”, each one is unique and deserves careful scrutiny.
Co-reporter:Elamparuthi Ramasamy, Nithyanandhan Jayaraj, Mintu Porel, and Vaidhyanathan Ramamurthy
Langmuir 2012 Volume 28(Issue 1) pp:10-16
Publication Date(Web):November 22, 2011
DOI:10.1021/la203419y
Synthesis and encapsulation properties of two new water-soluble resorcinol-capped organic cavitands (tetra acid and octa acid; RTA and ROA) are reported in this Letter. Organic guest molecules template the formation of capsular assembly of the above cavitands in water. Depending upon the guest, either 1:2 (guest to host) or 2:2 capsular assemblies were formed. The excited state properties of guests such as anthracene, camphorthione, and 4,4′-dimethyl benzil were distinctly different within a capsular assembly from those when they were free in a solution. Importantly, the host–guest complexes of the above two hosts (RTA and ROA) as well as octa acid (OA) could be transferred to a silica surface. The excited state behavior of host–guest assemblies on silica surface resembled that in solution. The high cage effect in the decarbonylation products and high yield of rearrangement product obtained upon photolysis of 1-phenyl-3-tolyl-2-propanone included within RTA, ROA, and OA both in solution and on silica surface supported the conclusion that capsular assemblies of these hosts are stable on silica surface.
Co-reporter:Shampa R. Samanta, Revathy Kulasekharan, Rajib Choudhury, Pradeepkumar Jagadesan, Nithyanandhan Jayaraj, and V. Ramamurthy
Langmuir 2012 Volume 28(Issue 32) pp:11920-11928
Publication Date(Web):July 18, 2012
DOI:10.1021/la302478e
In this report, we present methods of functionalization of AuNP's with deep-cavity cavitands that can include organic molecules. Two types of deep-cavity cavitand-functionalized AuNP's have been synthesized and characterized, one soluble in organic solvents and the other in water. Functionalized AuNP soluble in organic solvents forms a 1:1 host–guest complex where the guest is exposed to the exterior solvents. The one soluble in water forms a 2:1 host–guest complex where the guest is protected from solvent water. Phosphorescence from thiones and benzil included within heterocapsules attached to AuNP was quenched by gold atoms present closer to the guests included within deep-cavity cavitands. During this investigation, we have synthesized four new deep-cavity cavitands. Of these, two thiol-functionalized hosts allowed us to make stable AuNP's. However, AuNP's protected with two amine-functionalized cavitands tended to aggregate within a day.
Co-reporter:Revathy Kulasekharan and V. Ramamurthy
Organic Letters 2011 Volume 13(Issue 19) pp:5092-5095
Publication Date(Web):August 26, 2011
DOI:10.1021/ol201968w
Synthesis, inclusion properties, and ability to control excited-state properties of two water-soluble hosts are presented. These hosts surround the guest molecule(s) by forming a capsular assembly. By constraining the guest and by providing very little free space, the host is able to alter the excited-state behavior of guest molecules. The excited-state chemistry and physics of guest molecules are distinctly different from those in organic solvents.
Co-reporter:Shipra Gupta, Rajib Choudhury, Daniel Krois, Gerald Wagner, Udo H. Brinker, and V. Ramamurthy
Organic Letters 2011 Volume 13(Issue 22) pp:6074-6077
Publication Date(Web):October 27, 2011
DOI:10.1021/ol202568s
Chemical behavior of carbenes (adamantylidenes) generated by photolysis of adamantanediazirines has been investigated while they were incarcerated within an organic container in water and on silica surfaces. Confined carbenes behave differently from the free ones, and their behavior is dictated by the nature and the structure of the host–guest complexes. The substituent present on the adamantyl skeleton controls the stoichiometry (1:1 or 2:2) and the orientation of guest molecules within the host.
Co-reporter:Revathy Kulasekharan, Rajib Choudhury, Rajeev Prabhakar and V. Ramamurthy
Chemical Communications 2011 vol. 47(Issue 10) pp:2841-2843
Publication Date(Web):21 Jan 2011
DOI:10.1039/C0CC05337F
The rotational mobility of organic guest molecules when included within a confined capsule is restricted and this feature could be translated into product selectivity as established with the photochemical behavior of cyclohexyl phenyl ketones.
Co-reporter:Barnali Mondal, Burjor Captain and V. Ramamurthy
Photochemical & Photobiological Sciences 2011 vol. 10(Issue 6) pp:891-894
Publication Date(Web):05 Apr 2011
DOI:10.1039/C1PP05070B
A simple strategy that is based on conversion of an electron-rich pyridyl to an electron-deficient pyridinium ion is able to orient thirteen of the sixteen olefins investigated towards a single dimer in quantitative yield in the crystalline state. The reagent used is HCl, the method involves grinding the olefin with a drop of HCl and the dimerization is achieved by exposure of the crystalline stilbazolium·HCl salts to light. The weak force involved in modifying the crystal packing is most likely charge-transfer interaction.
Co-reporter:V. Ramamurthy;An Parthasarathy
Israel Journal of Chemistry 2011 Volume 51( Issue 7) pp:817-829
Publication Date(Web):
DOI:10.1002/ijch.201100065
Abstract
Carrying out chemical transformations under environmentally sustainable conditions has become one of the important current goals of chemistry. In this context, conducting reactions under solvent-free conditions (crystals, zeolites, clay, etc.) and in water has attracted considerable attention. Since most molecules either do not crystallize and or do not dissolve in water, the two approaches are complimentary. To make molecules solubilize in water one needs to employ water-soluble hosts such as micelles, cavitands, and capsules. To achieve selectivity, one should provide a confined environment within which the motions of reactant molecules are restricted to that in free solution. The confined space in which the reaction takes place independent of the host environment could be defined in terms of the “reaction cavity” originally presented by Cohen and Schmidt. In this mini-review, examples of photodimerization of olefins carried out in cavitands such as cucurbiturils, cyclodextrins, calixarenes, and octa acid are presented. Results are discussed in terms of the reaction cavity concept, which is applicable to reactions in both solids and water.
Co-reporter:Steffen Jockusch, Mintu Porel, V. Ramamurthy, and Nicholas J. Turro
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 22) pp:2877-2880
Publication Date(Web):October 26, 2011
DOI:10.1021/jz201328f
Thioxanthone and benzil derivatives were incarcerated into an octa acid nanocapsule. Photoexcitation of these ketones generated electronic triplet excited states, which become efficiently quenched by positively charged nitroxides adsorbed outside on the external surface of the negatively charged nanocapsule. Although the triplet excited ketone and quencher are separated by a molecular wall (nanocapsule), quenching occurs on the nanosecond time scale and generates spin-polarized nitroxides, which were observed by time-resolved EPR spectroscopy. Because opposite signs of spin polarization of nitroxides were observed for thioxanthone and benzil derivatives, it is proposed that the electron spin polarization transfer mechanism of spin-polarized triplet states to nitroxides is the major mechanism of generating nitroxide polarization.Keywords: laser flash photolysis; TEMPO; time-resolved EPR;
Co-reporter:Mintu Porel, Steffen Jockusch, M. Francesca Ottaviani, N. J. Turro, and V. Ramamurthy
Langmuir 2011 Volume 27(Issue 17) pp:10548-10555
Publication Date(Web):July 12, 2011
DOI:10.1021/la202120u
Communication between two molecules, one confined and excited (triplet or singlet) and one free and paramagnetic, has been explored through quenching of fluorescence and/or phosphorescence by nitroxides as paramagnetic radical species. Quenching of excited states by nitroxides has been investigated in solution, and the mechanism is speculated to involve charge transfer and/or exchange processes, both of which require close orbital interaction between excited molecule and quencher. We show in this report that such a quenching, which involves electron–electron spin communication, can occur even when there is a molecular wall between the two. The excited state molecule is confined within an organic capsule made up of two molecules of a deep cavity cavitand, octa acid, that exists in the anionic form in basic aqueous solution. The nitroxide is kept free in aqueous solution. 1H NMR and EPR experiments were carried out to ascertain the location of the two molecules. The distance between the excited molecule and the paramagnetic quencher was manipulated by the use of cationic, anionic, and neutral nitroxide and also by selectively including the cationic nitroxide within the cavity of cucurbituril. Results presented here highlight the role of the lifetime of the encounter complex in electron–electron spin communication when the direct orbital overlap between the two molecules is prevented by the intermediary wall.
Co-reporter:Anthony Baldridge ; Shampa R. Samanta ; Nithyanandhan Jayaraj ; V. Ramamurthy ;Laren M. Tolbert
Journal of the American Chemical Society 2010 Volume 133(Issue 4) pp:712-715
Publication Date(Web):December 21, 2010
DOI:10.1021/ja1094606
The turn-on of emission in fluorescent protein chromophores sequestered in an “octaacid” capsule is controlled by stereoelectronic effects described by a linear free energy relationship. The stereochemical effects are governed by both the positions and volumes of the aryl substituents, while the electronic effects, including ortho effects, can be treated with Hammett σ parameters. The use of substituent volumes rather than A values reflects packing of the molecule within the confines of the capsule.
Co-reporter:Balakrishna R. Bhogala ; Burjor Captain ; Anand Parthasarathy ;V. Ramamurthy
Journal of the American Chemical Society 2010 Volume 132(Issue 38) pp:13434-13442
Publication Date(Web):September 3, 2010
DOI:10.1021/ja105166d
In this study we have explored the potential of thiourea (TU) as a template to preorient stilbazoles and bispyridylethylenes (azastilbenes) in the crystalline state. TU is able to preorient eleven azastilbenes toward dimerization in the crystalline state. While cocrystals of these eleven olefins photodimerized to a single dimer expected based on crystal packing, pure crystals of these olefins either were nonreactive or gave a mixture of dimers. The differential photobehavior of the pure crystals and cocrystals highlights the importance of TU in templating the olefins in a photoreactive orientation in the crystalline state. X-ray crystallographic and photochemical studies have identified a few azastilbenes that photodimerize in spite of not being arranged in an ideal orientation in the crystalline state. These as well as a few examples already reported in the literature suggest that it is important to recognize that molecules could experience large amplitude motions in the crystalline state, especially when energized by light. Short-term lattice instability caused by photoexcitation can be effective in driving a photochemical reaction. Thus one should view the crystalline arrangement of molecules upon light exposure as “dynamic” rather than “static” as determined from X-ray structure analysis.
Co-reporter:Mintu Porel, Nithyanandhan Jayaraj, S. Raghothama, and V. Ramamurthy
Organic Letters 2010 Volume 12(Issue 20) pp:4544-4547
Publication Date(Web):September 24, 2010
DOI:10.1021/ol101841n
Propyloxy-substituted piperidine in solution adopts a conformation in which its alkoxy group is equatorially positioned. Surprisingly, two conformers of it that do not interconvert in the NMR time scale at room temperature have been found within an octa-acid capsule. The serendipitous finding of the axial conformer of propyloxy-substituted piperidine within a supramolecular capsule highlights the value of confined spaces in physical organic chemistry.
Co-reporter:Mintu Porel, M. Francesca Ottaviani, Steffen Jockusch, Nithyanandhan Jayaraj, Nicholas J. Turro and V. Ramamurthy
Chemical Communications 2010 vol. 46(Issue 41) pp:7736-7738
Publication Date(Web):20 Sep 2010
DOI:10.1039/C0CC02587A
The use of supramolecular architectures to control the spatially dependent spin exchange (spin communication) between two covalently linked radical centers (biradical) has been explored. Cucurbit[8]uril, through supramolecular steric effect, completely suppresses spin exchange between two adjacent radical centers in a biradical.
Co-reporter:Nithyanandhan Jayaraj, Murthy V. S. N. Maddipatla, Rajeev Prabhakar, Steffen Jockusch, N. J. Turro, and V. Ramamurthy
The Journal of Physical Chemistry B 2010 Volume 114(Issue 45) pp:14320-14328
Publication Date(Web):March 31, 2010
DOI:10.1021/jp911698s
Thiocarbonyl compounds possess unusual photophysical properties: they fluoresce from S2, phosphoresce from T1 only at extremely low concentrations in solution at room temperature, have unit quantum yield of intersystem crossing from S1 to T1, undergo self-quenching at diffusion-controlled rates, and are quenched by ground-state oxygen leading to self-destruction. In this article, we are concerned with finding a new method to observe phosphorescence from thioketones at room temperature in aqueous solution at high concentrations. To achieve this goal, one needs to find ways to eliminate diffusion-limited self-quenching and oxygen quenching. We present here a general strategy that has allowed us to record phopshorescence from a number of thioketones in aqueous solution at room temperature. The method involves encapsulation of thioketone molecules within a “closed nanocontainer” made up of two cavitand molecules known by its trivial name as octa acid. In these supramolecular complexes, despite two thiocarbonyl compounds being present in close proximity, no self-quenching occurs within the confined space due to curtailment of their rotational freedom. Although phosphorescence could also be observed when these thioketones are included in open containers, such as cucurbiturils and cyclodextrines, the closed container made up of octa acid is found to be the best medium to observe phosphorescence from thioketones whose excited state chemistry is essentially controlled by self-quenching.
Co-reporter:Revathy Kulasekharan, Nithyanandhan Jayaraj, Mintu Porel, Rajib Choudhury, Arun Kumar Sundaresan, Anand Parthasarathy, M. Francesca Ottaviani, Steffen Jockusch, N. J. Turro and V. Ramamurthy
Langmuir 2010 Volume 26(Issue 10) pp:6943-6953
Publication Date(Web):January 7, 2010
DOI:10.1021/la904196g
With the help of 1H NMR and EPR techniques, we have probed the dynamics of guest molecules included within a water-soluble deep cavity cavitand known by the trivial name octa acid. All guest molecules investigated here form 2:1 (host/guest) complexes in water, and two host molecules encapsulate the guest molecule by forming a closed capsule. We have probed the dynamics of the guest molecule within this closed container through 1H NMR and EPR techniques. The timescales offered by these two techniques are quite different, millisecond and nanosecond, respectively. For EPR studies, paramagnetic nitroxide guest molecules and for 1H NMR studies, a wide variety of structurally diverse neutral organic guest molecules were employed. The guest molecules freely rotate along their x axis (long molecular axis and magnetic axis) on the NMR timescale; however, their rotation is slowed with respect to that in water on the EPR timescale. Rotation along the x axis is dependent on the length of the alkyl chain attached to the nitroxide probe. Overall rotation along the y or z axis was very much dependent on the structure of the guest molecule. The guests investigated could be classified into three groups: (a) those that do not rotate along the y or z axis both at room and elevated (55 °C) temperatures, (b) those that rotate freely at room temperature, and (c) those that do not rotate at room temperature but do so at higher temperatures. One should note that rotation here refers to the NMR timescale and it is quite possible that all molecules may rotate at much longer timescales than the one probed here. A slight variation in structure alters the rotational mobility of the guest molecules.
Co-reporter:Steffen Jockusch, Olaf Zeika, Nithyanandhan Jayaraj, V. Ramamurthy, and Nicholas J. Turro
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 18) pp:2628-2632
Publication Date(Web):August 20, 2010
DOI:10.1021/jz101006s
A thioxanthone derivative containing a covalently attached 15N-labeled nitroxide was incarcerated into an octaacid nanocapsule. Photoexcitation of the thioxanthone chromophore generated electron spin polarization of the nitroxide. This spin polarization of the 15N-labeled nitroxide was transferred through the walls of the carcerand to a 14N-labeled nitroxide in external bulk solvent, a process that was directly observed by time-resolved EPR spectroscopy. The efficiency of the communication between the incarcerated guest and molecules in the bulk solvent was shown to be controlled by supramolecular factors such as Coulombic attraction and repulsion between the guest@host complex and charged molecules in the bulk solvent phase.Keywords (keywords): cucurbituril; laser flash photolysis; superexchange; TEMPO; time-resolved EPR;
Co-reporter:Arun Kumar Sundaresan, Lakshmi S. Kaanumalle, Corinne L. D. Gibb, Bruce C. Gibb and V. Ramamurthy
Dalton Transactions 2009 (Issue 20) pp:4003-4011
Publication Date(Web):31 Mar 2009
DOI:10.1039/B900017H
The value of a supramolecular assembly to enforce a closer interaction between a chiral auxiliary and a reaction center has been established using photoreactions of tropolone and cyclohexadienone derivatives. Two probe molecules utilized to establish the concept undergo 4 e− electrocyclization and oxa-di-π-methane rearrangement from excited singlet and triplet state, respectively. The chiral auxiliaries investigated here has no/little effect in acetonitrile solution during phototransformations of the probe molecules to yield products with new chiral centers. On the other hand the same ones are able to enforce diastereoselectivities to the extent of ∼30% when the reactions occur within the restricted space of a capsule made up of a synthetic cavitand commonly known as octa acid. Extensive NMR studies have been utilized to characterize the guest–host supramolecular structures. The results presented here should be of value in the overall understanding of chiral induction in photochemical reactions.
Co-reporter:Raja Kaliappan, V. Ramamurthy
Journal of Photochemistry and Photobiology A: Chemistry 2009 Volume 207(Issue 1) pp:32-37
Publication Date(Web):5 September 2009
DOI:10.1016/j.jphotochem.2008.10.004
This publication pertains to the exploration of supramolecular assemblies to control excited state chemistry. One of our long-range scientific goals is to develop, on the basis of well-established rules of molecular organic photochemistry and supramolecular chemistry, a model to predict the photobehavior of organic molecules in restricted spaces, in general. We present the results of our studies on the photochemistry of benzoin alkyl ethers included within calixarenes in water. While in isotropic solution benzoin alkyl ethers yield products of Norrish Type I reaction, as guest–host complex with calixarenes they preferentially yield products of Norrish Type II reaction. The current observation suggests that rules of physical organic chemistry and photochemistry developed based on solution chemistry cannot be simply extended to supramolecular assemblies.
Co-reporter:Mintu Porel, Nithyanandhan Jayaraj, Lakshmi S. Kaanumalle, Murthy V. S. N. Maddipatla, Anand Parthasarathy and V. Ramamurthy
Langmuir 2009 Volume 25(Issue 6) pp:3473-3481
Publication Date(Web):February 16, 2009
DOI:10.1021/la804194w
We have been exploring the use of a deep cavity cavitand known by the trivial name ‘octa acid’ as a photochemical reaction cavity for manipulating photochemical and photophysical properties of organic molecules. In the current study, we have monitored the micropolarity of the interior of the cavitand by recording the fluorescence of five different organic probes. They all indicate that the interior of octa acid capsuleplex (2:1, H/G complex) is nonpolar and does not contain water molecules in spite of the complex being present in water. The nature of the octa acid−probe complex in each case has been characterized by 1H NMR data to be a 2:1 capsuleplex. Photophysical and 1H NMR experiments were employed to probe the factors that control the structure of the complex, 2:2, 2:1, and 1:1. The data we have on hand suggest that the structure of the host/guest complex depends on the size and hydrophobicity of the guest molecule.
Co-reporter:Raja Kaliappan, Yonghua Ling, Angel E. Kaifer and V. Ramamurthy
Langmuir 2009 Volume 25(Issue 16) pp:8982-8992
Publication Date(Web):April 9, 2009
DOI:10.1021/la900659r
Smaller members of water-soluble sulfonated calixarenes have been extensively explored in the context of host−guest complexation, supramolecular chemistry, and potential sensors. However, larger members especially eight-membered calixarene (CA[8]) has received much less attention because of its floppy nature and tendency to exist as a mixture of conformational isomers. Our continued interest in identifying molecules with an internal cavity as reaction vessels has led us to examine the host−guest complexation of CA[8] with photoactive bispyridyl ethylenes. We find that 4,4′-bispyridyl ethylene and 3,3′-bispyridyl ethylene upon complexation to CA[8] arrest the conformational equilibrium and force the latter to adopt a single conformation in solution. During complexation, bispyridyl ethylenes are protonated by the sulfonic acid groups of CA[8]. The host−guest complex is stabilized via an electrostatic interaction between the cationic bispyridyl ethylenes and anionic sulfonated calix[8]arene, and we propose the complex to have an inverted capsular structure. This model is also consistent with the electrochemical behavior of 4,4′-dimethylviologen included within CA[8]. Rigidification of bispyridyl ethylenes by the host has a consequence on the excited-state chemistry of the former. Generally, prevalent geometric isomerization of bispyridyl ethylenes are prevented by CA[8] upon complexation.
Co-reporter:Nithyanandhan Jayaraj, Mintu Porel, M. Francesca Ottaviani, Murthy V. S. N. Maddipatla, Alberto Modelli, José P. Da Silva, Balakrishna R. Bhogala, Burjor Captain, Steffen Jockusch, Nicholas J. Turro and V. Ramamurthy
Langmuir 2009 Volume 25(Issue 24) pp:13820-13832
Publication Date(Web):August 14, 2009
DOI:10.1021/la9020806
Supramolecular complexation behavior of cucurbiturils with paramagnetic nitroxide spin probes was examined by 1H NMR, X-ray diffraction studies of crystals, computation, and EPR. Both cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) form a 1:1 complex with 4-(N,N,N-trimethylammonium)-2,2,6,6-tetramethylpiperidinyl-N-oxy bromide (CAT1). The structure of the complex in the solid state was inferred by X-ray diffraction studies and in the gas phase by computation (B3LYP/6-31G(d)). Whereas ESI-MS data provided evidence for the existence of the complex in solution, indirect evidence was obtained through 1H NMR studies with a structural diamagnetic analogue, 4-(N,N,N-trimethylammonium)-2,2,6,6-tetramethyl-N-methylpiperidine iodide (DCAT1). The EPR spectrum of the CAT1@CB7 complex consisting of three lines suggested that probe CAT1 is associated with host CB7 such that the nitroxide part is exposed to water. The spectral pattern was independent of the concentration of the complex and the presence of salt such as NaCl. The most interesting observation was made with CB8 as the host. In this case, in addition to the expected three-line spectrum, an additional spectrum consisting of seven lines was recorded. The contribution of the seven-line spectrum to the total spectrum was dependent on the concentration of the complex and added salt (NaCl) to the aqueous solution. The coupling constant for the seven-line spectrum for 14N-substituted CAT1 is 5 G, and that for the four-line spectrum for 15N-substituted CAT1 is 7.15 G. The only manner by which we could reproduce the observed spectra by simulation for both 14N- and 15N-substituted CAT1@CB8 was by assuming a spin exchange among three nitroxide radicals. To account for this observation, we hypothesize that three CAT1 molecules included within CB8 interact in such a way that there is an association of three supramolecules of CAT1@CB8 (i.e., [CAT1@CB8]3) in a triangular geometry that leads to spin exchange between the three radical centers. We have established, with the help of 13 additional examples, that this is a general phenomenon. We are in the process of understanding this unusual phenomenon.
Co-reporter:Nithyanandhan Jayaraj, Yaopeng Zhao, Anand Parthasarathy, Mintu Porel, Robert S. H. Liu and V. Ramamurthy
Langmuir 2009 Volume 25(Issue 18) pp:10575-10586
Publication Date(Web):June 4, 2009
DOI:10.1021/la901367k
Factors that govern inclusion of organic molecules within octa acid (OA), a synthetic deep cavity cavitand, have been delineated by examining the complexation behavior of a number of organic molecules with varying dimensions and functionalities with OA. The formation of two types of complexes has been noted: the one which we call cavitandplex is a partially open complex in which a part of the guest molecule remains exposed to water, and the other termed capsuleplex is formed through assembly of two OA molecules. In capsuleplex, the guest is protected from water. Generally, guest molecules that possess ionic head groups form cavitandplex, and all others form capsuleplex. Capsuleplex may contain one or two guest molecules within the capsule. Small organic molecules (<10 Å in length) may form both 2:1 and 2:2 capsuleplex, while longer ones (>12 Å) preferentially form 2:1 capsuleplex. Extensive 1H NMR experiments have been carried out to characterize host−guest complexes. In the absence of the guest, OA tends to aggregate in water. The extent of aggregation depends on the concentration of OA and the presence of salts in solution. We expect the information obtained from this study to be of great value in predicting the nature of complexes with a given guest and facilitating appropriate guest chosen by researchers.
Co-reporter:Raja Kaliappan, V. Ramamurthy
Journal of Photochemistry and Photobiology A: Chemistry 2009 Volume 207(Issue 1) pp:144-152
Publication Date(Web):5 September 2009
DOI:10.1016/j.jphotochem.2009.03.004
Chiral induction in products resulting from hydrogen abstraction upon excitation of carbonyl compounds included in four cyclodextrin related host systems has been examined. The chiral induction obtained in photoproducts is moderate. Results suggest that there is potential to improve the asymmetric interaction between the reactant molecules and the supramolecular host cyclodextrins. However, no models that would help us to predict the outcome of chiral induction in a photochemical reaction have resulted from this investigation. Given the use of cyclodextrins as chiral stationary phases in HPLC and GC separations we are optimistic that there is considerable potential for cyclodextrins as chiral hosts in photoreactions.
Co-reporter:Arun Kumar Sundaresan, Corinne L.D. Gibb, Bruce C. Gibb, V. Ramamurthy
Tetrahedron 2009 65(35) pp: 7277-7288
Publication Date(Web):
DOI:10.1016/j.tet.2009.01.110
Co-reporter:Lakshmi S. Kaanumalle and V. Ramamurthy
Chemical Communications 2007 (Issue 10) pp:1062-1064
Publication Date(Web):14 Dec 2006
DOI:10.1039/B615937K
Direct excitation of acenaphthylene molecules included in a syn fashion within the octa acid nanocapsule dimerizes quantitatively to a syn dimer, and upon triplet sensitization, yields both syn and anti dimers probably by reacting within and outside the capsule.
Co-reporter:Lakshmi S. Kaanumalle, Corinne L. D. Gibb, Bruce C. Gibb and V. Ramamurthy
Organic & Biomolecular Chemistry 2007 vol. 5(Issue 2) pp:236-238
Publication Date(Web):29 Nov 2006
DOI:10.1039/B617022F
The water soluble capsule formed by a deep cavity cavitand with eight carboxylic acid groups controls product distribution during photo-Fries rearrangement of naphthyl esters in water by restricting the mobility of primary singletradical pair.
Co-reporter:Raja Kaliappan, Murthy V. S. N. Maddipatla, Lakshmi S. Kaanumalle and V. Ramamurthy
Photochemical & Photobiological Sciences 2007 vol. 6(Issue 7) pp:737-740
Publication Date(Web):15 Jun 2007
DOI:10.1039/B704817C
Borrowing concepts from crystal engineering techniques we have been able to steer the photodimerization of stilbazolium salts included in γ-cyclodextrin towards a desired dimer.
Co-reporter:Selvanathan Arumugam, Dharma Rao Vutukuri, S. Thayumanavan, V. Ramamurthy
Journal of Photochemistry and Photobiology A: Chemistry 2007 Volume 185(2–3) pp:168-171
Publication Date(Web):25 January 2007
DOI:10.1016/j.jphotochem.2006.05.032
A styrene based water soluble polymer (polymer-A) has been explored as a host for solubilizing otherwise insoluble aromatic hydrocarbons in water. The increased local concentration of encapsulated aromatic hydrocarbons within the hydrophobic pockets of polymer-A was utilized for performing efficient photodimerization of acenaphthylene (1) and six 9-substituted anthracenes [AnCOOH, AnCHO, AnCH2OH, AnCH3, AnBr and AnCN] in water. Photodimerization of these aromatic hydrocarbons were more efficient than in water and yielded dimers even at low concentrations (∼10−4 M). At the same concentration of anthracenes in organic solvents such as benzene and methanol, no dimers were formed even after 48 h of irradiation. Although the polymer-A was able to increase the local concentration of the reactant aromatics it was unable to orient them towards a single dimer.
Co-reporter:J. Shailaja, Lakshmi S. Kaanumalle, Karthikeyan Sivasubramanian, Arunkumar Natarajan, Keith J. Ponchot, Ajit Pradhan and V. Ramamurthy
Organic & Biomolecular Chemistry 2006 vol. 4(Issue 8) pp:1561-1571
Publication Date(Web):14 Mar 2006
DOI:10.1039/B517069A
Photochemistry of 17 aryl alkyl ketones included within cation exchanged zeolites has been examined. In solution five of the 17 ketones undergo intramolecular hydrogen abstraction reaction even in the presence of a chiral amine and the rest are photoreduced to the corresponding alcohol. Within zeolites all 17 ketones yielded in presence of a chiral amine, the corresponding alcohol as the major product. When a chiral amine was used as the coadsorbent within alkali ion exchanged zeolites, enantiomerically enriched alcohol was formed in all cases. The best chiral induction was obtained with phenyl cyclohexyl ketone (enantiomeric excess: 68%). 1H–13C Cross Polarization Magic Angle Spinning (CP-MAS) experiments, with a model ketone (perdeuterated acetophenone) and chiral amine (pseudoephedrine) included within MY zeolites, suggested that the cation brings the reactant and the chiral amine closer. The role of the cation in such a process is also revealed by the computation results. The results presented here highlight the importance of a supramolecular structure in forcing a closer interaction between a reactant and a chiral inductor that could be used to achieve asymmetric induction in photoproducts.
Co-reporter:Selvanathan Arumugam;Lakshmi S. Kaanumalle;V. Ramamurthy
Photochemistry and Photobiology 2006 Volume 82(Issue 1) pp:139-145
Publication Date(Web):30 APR 2007
DOI:10.1562/2005-05-05-RA-515
Methanol-swollen Nafion beads were used as microreactors to control the photochemical reaction pathways. Product selectivity in three unimolecular reactions, namely, the photo-Fries rearrangement of naphthyl esters, Norrish Type I reaction of 1-phenyl-3-p-tolyl-propan-2-one and Norrish Type I and Type II reactions of benzoin alkyl ethers were examined. The influence of cations over the photodimerization of acenaphthylene and cross-photodimerization between acenaphthylene and N-benzyl maleimide included within Nafion were also examined. The photochemical behaviors of the above substrates were significantly altered within Nafion compared with their solution photochemistry. Of particular interest, the product distributions were found to depend on the counter cations of Nafion.
Co-reporter:Raja Kaliappan, Lakshmi S. Kaanumalle, Arunkumar Natarajan and V. Ramamurthy
Photochemical & Photobiological Sciences 2006 vol. 5(Issue 10) pp:925-930
Publication Date(Web):15 Aug 2006
DOI:10.1039/B606658E
Water soluble six and eight membered calixarenes template the dimerization of trans-stilbazoles. In the absence of calixarenes at the concentrations employed stilbazoles mainly isomerize to the coresponding cis isomers. Calixarenes help to localize the olefins and orient them in a specific geometry to yield anti-head–tail dimers. Electrostatic interaction between the sulfonate anion and the pyridinium ion of the olefin and hydrophobic interaction between the olefin and the host cavity are believed to be responsible for the observed selectivity. 1H NMR spectra provide evidence for complexation but do not suggest the exact structure of the host–guest complex.
Co-reporter:Mahesh Pattabiraman, Arunkumar Natarajan, Raja Kaliappan, Joel T. Mague and V. Ramamurthy
Chemical Communications 2005 (Issue 36) pp:4542-4544
Publication Date(Web):11 Aug 2005
DOI:10.1039/B508458J
Template induced photodimerization of trans-1,2-bis(n-pyridyl)ethylene dihydrochlorides and trans-n-stilbazole hydrochlorides within cucurbit[8]uril in aqueous media leads to high yields of the syn dimer.
Co-reporter:Raja Kaliappan, Lakshmi S. Kaanumalle and V. Ramamurthy
Chemical Communications 2005 (Issue 32) pp:4056-4058
Publication Date(Web):13 Jul 2005
DOI:10.1039/B507517C
Benzoin alkyl ethers encapsulated in a cisoid conformation within water-soluble p-sulfonatocalix[8]arenes preferentially yield the Norrish Type II reaction product deoxybenzoin.
Co-reporter:Abraham Joy, Lakshmi S. Kaanumalle and V. Ramamurthy
Organic & Biomolecular Chemistry 2005 vol. 3(Issue 16) pp:3045-3053
Publication Date(Web):13 Jul 2005
DOI:10.1039/B504865F
Asymmetric induction in photochemical reactions has been explored using the photochemistry of tropolones as a model. Three approaches have been examined: chiral inductor, chiral auxiliary and [chiral inductor + chiral auxiliary]. All three methods gave excellent asymmetric induction in zeolite and very little or zero induction in solution. Results presented on tropolones clearly illustrate the remarkable influence that a confined space studded with cations can have on asymmetric induction. Tropolone derivatives, upon irradiation undergo 4π-electron electrocyclization to yield a bicyclic product and a rearranged product. Enantiomeric excess up to 68% has been achieved in the cyclized product. In systems where a chiral inductor has been covalently linked, diastereomeric excess as high as 88% has been achieved within a zeolite while the same system in solution gave 10%.
Co-reporter:Lakshmi S. Kaanumalle and V. Ramamurthy
Chemical Communications 2007(Issue 10) pp:NaN1064-1064
Publication Date(Web):2006/12/14
DOI:10.1039/B615937K
Direct excitation of acenaphthylene molecules included in a syn fashion within the octa acid nanocapsule dimerizes quantitatively to a syn dimer, and upon triplet sensitization, yields both syn and anti dimers probably by reacting within and outside the capsule.
Co-reporter:Lakshmi S. Kaanumalle, Corinne L. D. Gibb, Bruce C. Gibb and V. Ramamurthy
Organic & Biomolecular Chemistry 2007 - vol. 5(Issue 2) pp:NaN238-238
Publication Date(Web):2006/11/29
DOI:10.1039/B617022F
The water soluble capsule formed by a deep cavity cavitand with eight carboxylic acid groups controls product distribution during photo-Fries rearrangement of naphthyl esters in water by restricting the mobility of primary singletradical pair.
Co-reporter:Revathy Kulasekharan, Rajib Choudhury, Rajeev Prabhakar and V. Ramamurthy
Chemical Communications 2011 - vol. 47(Issue 10) pp:NaN2843-2843
Publication Date(Web):2011/01/21
DOI:10.1039/C0CC05337F
The rotational mobility of organic guest molecules when included within a confined capsule is restricted and this feature could be translated into product selectivity as established with the photochemical behavior of cyclohexyl phenyl ketones.
Co-reporter:Mintu Porel, M. Francesca Ottaviani, Steffen Jockusch, Nithyanandhan Jayaraj, Nicholas J. Turro and V. Ramamurthy
Chemical Communications 2010 - vol. 46(Issue 41) pp:NaN7738-7738
Publication Date(Web):2010/09/20
DOI:10.1039/C0CC02587A
The use of supramolecular architectures to control the spatially dependent spin exchange (spin communication) between two covalently linked radical centers (biradical) has been explored. Cucurbit[8]uril, through supramolecular steric effect, completely suppresses spin exchange between two adjacent radical centers in a biradical.
Co-reporter:Takuya Fujimura, Elamparuthi Ramasamy, Yohei Ishida, Tetsuya Shimada, Shinsuke Takagi and Vaidhyanathan Ramamurthy
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 7) pp:NaN5411-5411
Publication Date(Web):2016/01/12
DOI:10.1039/C5CP06984J
To achieve the goal of energy transfer and subsequent electron transfer across three molecules, a phenomenon often utilized in artificial light harvesting systems, we have assembled a light absorber (that also serves as an energy donor), an energy acceptor (that also serves as an electron donor) and an electron acceptor on the surface of an anionic clay nanosheet. Since neutral organic molecules have no tendency to adsorb onto the anionic surface of clay, a positively charged water-soluble organic capsule was used to hold neutral light absorbers on the above surface. A three-component assembly was prepared by the co-adsorption of a cationic bipyridinium derivative, cationic zinc porphyrin and cationic octaamine encapsulated 2-acetylanthracene on an exfoliated anionic clay surface in water. Energy and electron transfer phenomena were monitored by steady state fluorescence and picosecond time resolved fluorescence decay. The excitation of 2-acetylanthracene in the three-component system resulted in energy transfer from 2-acetylanthracene to zinc porphyrin with 71% efficiency. Very little loss due to electron transfer from 2-acetylanthracene in the cavitand to the bipyridinium derivative was noticed. Energy transfer was followed by electron transfer from the zinc porphyrin to the cationic bipyridinium derivative with 81% efficiency. Analyses of fluorescence decay profiles confirmed the occurrence of energy transfer and subsequent electron transfer. Merging the concepts of supramolecular chemistry and surface chemistry we realized sequential energy and electron transfer between three hydrophobic molecules in water. Exfoliated transparent saponite clay served as a matrix to align the three photoactive molecules at a close distance in aqueous solutions.
Co-reporter:Arun Kumar Sundaresan, Lakshmi S. Kaanumalle, Corinne L. D. Gibb, Bruce C. Gibb and V. Ramamurthy
Dalton Transactions 2009(Issue 20) pp:NaN4011-4011
Publication Date(Web):2009/03/31
DOI:10.1039/B900017H
The value of a supramolecular assembly to enforce a closer interaction between a chiral auxiliary and a reaction center has been established using photoreactions of tropolone and cyclohexadienone derivatives. Two probe molecules utilized to establish the concept undergo 4 e− electrocyclization and oxa-di-π-methane rearrangement from excited singlet and triplet state, respectively. The chiral auxiliaries investigated here has no/little effect in acetonitrile solution during phototransformations of the probe molecules to yield products with new chiral centers. On the other hand the same ones are able to enforce diastereoselectivities to the extent of ∼30% when the reactions occur within the restricted space of a capsule made up of a synthetic cavitand commonly known as octa acid. Extensive NMR studies have been utilized to characterize the guest–host supramolecular structures. The results presented here should be of value in the overall understanding of chiral induction in photochemical reactions.
Co-reporter:V. Ramamurthy and Shipra Gupta
Chemical Society Reviews 2015 - vol. 44(Issue 1) pp:NaN135-135
Publication Date(Web):2014/10/15
DOI:10.1039/C4CS00284A
Photochemical and photophysical behavior of molecules in supramolecular assemblies are different and more selective than in gas and isotropic solution phases. Knowledge of the inherent electronic and steric properties of the reactant is insufficient to predict the excited state behavior of molecules confined in such assemblies. Weak interactions between the medium and the reactant as well as the free space in a reaction cavity would play a significant role in modulating the excited state properties of molecules when they are included within confined spaces. The concepts of ‘Molecular Photochemistry’ should be modified while applying them to ‘Supramolecular Photochemistry’. In this review we show that the topochemical rules established to understand reactions in crystals could be extended to supramolecular assemblies in general. To make the best use of the medium one needs to understand the features of the medium, the nature of interaction between the medium and the molecule and the rules that govern the behavior of a molecule in that medium. This tutorial provides introduction to these aspects of ‘Supramolecular Photochemistry’.
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![Acetamide, 2-bromo-N-[(1S)-1-phenylethyl]-](http://img.cochemist.com/ccimg/194000/193967-71-4.png)
![Acetamide, 2-bromo-N-[(1S)-1-phenylethyl]-](http://img.cochemist.com/ccimg/194000/193967-71-4_b.png)
![Acetamide, 2-bromo-N-[(1R)-1-phenylethyl]-](http://img.cochemist.com/ccimg/166800/166771-57-9.png)
![Acetamide, 2-bromo-N-[(1R)-1-phenylethyl]-](http://img.cochemist.com/ccimg/166800/166771-57-9_b.png)
![Benzonitrile, 4-[(1Z)-2-(1-pyrenyl)ethenyl]-](http://img.cochemist.com/ccimg/159400/159394-70-4.png)
![Benzonitrile, 4-[(1Z)-2-(1-pyrenyl)ethenyl]-](http://img.cochemist.com/ccimg/159400/159394-70-4_b.png)
![1-Azaspiro[3.5]nonan-2-one, 3-hydroxy-1-(1-methylethyl)-3-phenyl-](http://img.cochemist.com/ccimg/150800/150781-99-0.png)
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![Benzonitrile, 4-[(1E)-2-(1-pyrenyl)ethenyl]-](http://img.cochemist.com/ccimg/149900/149849-38-7.png)
![Benzonitrile, 4-[(1E)-2-(1-pyrenyl)ethenyl]-](http://img.cochemist.com/ccimg/149900/149849-38-7_b.png)
![Pyrene, 1-[(1E)-2-(4-nitrophenyl)ethenyl]-](http://img.cochemist.com/ccimg/149900/149849-37-6.png)
![Pyrene, 1-[(1E)-2-(4-nitrophenyl)ethenyl]-](http://img.cochemist.com/ccimg/149900/149849-37-6_b.png)
![4H-1-Benzopyran-4-one, 2-[4-(diethylamino)phenyl]-3-hydroxy-](http://img.cochemist.com/ccimg/146700/146680-78-6.png)
![4H-1-Benzopyran-4-one, 2-[4-(diethylamino)phenyl]-3-hydroxy-](http://img.cochemist.com/ccimg/146700/146680-78-6_b.png)
![1-Azaspiro[3.5]nonan-2-one, 1-cyclohexyl-3-hydroxy-3-phenyl-](http://img.cochemist.com/ccimg/143100/143086-96-8.png)
![1-Azaspiro[3.5]nonan-2-one, 1-cyclohexyl-3-hydroxy-3-phenyl-](http://img.cochemist.com/ccimg/143100/143086-96-8_b.png)
![Pyridine, 4-[2-(3,4-dimethoxyphenyl)ethenyl]-, (E)-](/data/chemimg/1093100/138499-81-7.png)
![Pyridine, 4-[2-(3,4-dimethoxyphenyl)ethenyl]-, (E)-](/data/chemimg/1093100/138499-81-7_b.png)
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![Fluoranthene, 8-[(1Z)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/126900/126831-75-2.png)
![Fluoranthene, 8-[(1Z)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/126900/126831-75-2_b.png)
![Fluoranthene, 8-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/126900/126831-74-1.png)
![Fluoranthene, 8-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/126900/126831-74-1_b.png)
![Methanone, [4-[(1-methylethoxy)methyl]phenyl]phenyl-](http://img.cochemist.com/ccimg/119600/119557-91-4.png)
![Methanone, [4-[(1-methylethoxy)methyl]phenyl]phenyl-](http://img.cochemist.com/ccimg/119600/119557-91-4_b.png)
![Benzene, 1,1'-[1,2-bis(octyloxy)-1,2-ethanediyl]bis-](http://img.cochemist.com/ccimg/109400/109391-44-8.png)
![Benzene, 1,1'-[1,2-bis(octyloxy)-1,2-ethanediyl]bis-](http://img.cochemist.com/ccimg/109400/109391-44-8_b.png)
![Methanamine, N-[(2-bromophenyl)methylene]-](http://img.cochemist.com/ccimg/95600/95547-10-7.png)
![Methanamine, N-[(2-bromophenyl)methylene]-](http://img.cochemist.com/ccimg/95600/95547-10-7_b.png)
![METHANAMINE, N-[(3-CHLOROPHENYL)METHYLENE]-](http://img.cochemist.com/ccimg/90500/90434-25-6.png)
![METHANAMINE, N-[(3-CHLOROPHENYL)METHYLENE]-](http://img.cochemist.com/ccimg/90500/90434-25-6_b.png)
![2,4-Methano-4H-cycloprop[cd]inden-4-ol, hexahydro-](http://img.cochemist.com/ccimg/90200/90125-38-5.png)
![2,4-Methano-4H-cycloprop[cd]inden-4-ol, hexahydro-](http://img.cochemist.com/ccimg/90200/90125-38-5_b.png)
![Pyridine, 4-[(1E)-2-(4-bromophenyl)ethenyl]-](/data/chemimg/1966500/75990-92-0.png)
![Pyridine, 4-[(1E)-2-(4-bromophenyl)ethenyl]-](/data/chemimg/1966500/75990-92-0_b.png)
![Pyrene, 1-[(1Z)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/75100/75005-51-5.png)
![Pyrene, 1-[(1Z)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/75100/75005-51-5_b.png)
![Pyrene, 1-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/73300/73249-33-9.png)
![Pyrene, 1-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/73300/73249-33-9_b.png)
![4-Azatricyclo[4.3.1.13,8]undec-4-ene](http://img.cochemist.com/ccimg/65300/65218-91-9.png)
![4-Azatricyclo[4.3.1.13,8]undec-4-ene](http://img.cochemist.com/ccimg/65300/65218-91-9_b.png)
![2H-1-Benzopyran-2-one, 4-[(acetyloxy)methyl]-7-methoxy-](http://img.cochemist.com/ccimg/61000/60951-30-6.png)
![2H-1-Benzopyran-2-one, 4-[(acetyloxy)methyl]-7-methoxy-](http://img.cochemist.com/ccimg/61000/60951-30-6_b.png)
![2-PROPENOIC ACID, 3-[2-(2-PROPENYLOXY)PHENYL]-, (2Z)-](http://img.cochemist.com/ccimg/60400/60326-22-9.png)
![2-PROPENOIC ACID, 3-[2-(2-PROPENYLOXY)PHENYL]-, (2Z)-](http://img.cochemist.com/ccimg/60400/60326-22-9_b.png)
![1-Propanamine, N-[(2-chlorophenyl)methylene]-](http://img.cochemist.com/ccimg/58700/58645-99-1.png)
![1-Propanamine, N-[(2-chlorophenyl)methylene]-](http://img.cochemist.com/ccimg/58700/58645-99-1_b.png)
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![4-azatricyclo[4.3.1.1~3,8~]undecan-3-ol](http://img.cochemist.com/ccimg/55100/55086-02-7_b.png)
![Benzene, 1-methyl-2-[(1Z)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/53500/53423-25-9.png)
![Benzene, 1-methyl-2-[(1Z)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/53500/53423-25-9_b.png)
![Bicyclo[2.2.1]heptane-2-thione, 1,7,7-trimethyl-, (1S,4S)-](http://img.cochemist.com/ccimg/52100/52078-93-0.png)
![Bicyclo[2.2.1]heptane-2-thione, 1,7,7-trimethyl-, (1S,4S)-](http://img.cochemist.com/ccimg/52100/52078-93-0_b.png)
![Lithium, [[bis(1-methylethyl)amino]carbonyl]-](http://img.cochemist.com/ccimg/51900/51804-79-6.png)
![Lithium, [[bis(1-methylethyl)amino]carbonyl]-](http://img.cochemist.com/ccimg/51900/51804-79-6_b.png)
![BENZENE, 1,1'-[1,2-BIS(1-METHYLETHOXY)-1,2-ETHANEDIYL]BIS-](http://img.cochemist.com/ccimg/49600/49593-34-2.png)
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![BENZO[LMN][3,8]PHENANTHROLINIUM, 2,7-DIMETHYL-](http://img.cochemist.com/ccimg/46900/46860-67-7_b.png)
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![METHANONE, PHENYLTRICYCLO[3.3.1.1(3,7)]DEC-1-YL-](http://img.cochemist.com/ccimg/32000/31919-47-8_b.png)
![Ethanone,1-phenyl-2-tricyclo[3.3.1.13,7]dec-1-yl-](http://img.cochemist.com/ccimg/27700/27648-26-6.png)
![Ethanone,1-phenyl-2-tricyclo[3.3.1.13,7]dec-1-yl-](http://img.cochemist.com/ccimg/27700/27648-26-6_b.png)
![Tricyclo[3.3.1.13,7]decane, 1-azido-](/data/chemimg/409500/24886-73-5.png)
![Tricyclo[3.3.1.13,7]decane, 1-azido-](/data/chemimg/409500/24886-73-5_b.png)
![Benzene, 1-ethyl-4-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/24900/24840-11-7.png)
![Benzene, 1-ethyl-4-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/24900/24840-11-7_b.png)
![Benzene, 1-methyl-2-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/22300/22257-16-5.png)
![Benzene, 1-methyl-2-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/22300/22257-16-5_b.png)
![Benzene, 1-methyl-2-[(4-methylphenyl)methyl]-](http://img.cochemist.com/ccimg/21900/21895-17-0.png)
![Benzene, 1-methyl-2-[(4-methylphenyl)methyl]-](http://img.cochemist.com/ccimg/21900/21895-17-0_b.png)
![Bicyclo[3.2.0]hepta-3,6-dien-2-one, 7-methoxy-](http://img.cochemist.com/ccimg/20800/20764-21-0.png)
![Bicyclo[3.2.0]hepta-3,6-dien-2-one, 7-methoxy-](http://img.cochemist.com/ccimg/20800/20764-21-0_b.png)
![Pyridine, 4-[(1Z)-2-(1-naphthalenyl)ethenyl]-](http://img.cochemist.com/ccimg/20200/20111-31-3.png)
![Pyridine, 4-[(1Z)-2-(1-naphthalenyl)ethenyl]-](http://img.cochemist.com/ccimg/20200/20111-31-3_b.png)
![Benzene, 1-methyl-3-[(1Z)-2-phenylethenyl]-](/data/chemimg/1779000/19466-29-6.png)
![Benzene, 1-methyl-3-[(1Z)-2-phenylethenyl]-](/data/chemimg/1779000/19466-29-6_b.png)
![Bicyclo[3.2.0]hepta-3,6-dien-2-one, 1-methoxy-](http://img.cochemist.com/ccimg/18500/18455-03-3.png)
![Bicyclo[3.2.0]hepta-3,6-dien-2-one, 1-methoxy-](http://img.cochemist.com/ccimg/18500/18455-03-3_b.png)
![Spiro[2H-1-benzopyran-2,2'-[2H]indole], 6-bromo-1',3'-dihydro-1',3',3'-trimethyl-](/data/chemimg/914700/16650-14-9.png)
![Spiro[2H-1-benzopyran-2,2'-[2H]indole], 6-bromo-1',3'-dihydro-1',3',3'-trimethyl-](/data/chemimg/914700/16650-14-9_b.png)
![Pyridine, 4-[(1E)-2-(1-naphthalenyl)ethenyl]-](http://img.cochemist.com/ccimg/16400/16375-78-3.png)
![Pyridine, 4-[(1E)-2-(1-naphthalenyl)ethenyl]-](http://img.cochemist.com/ccimg/16400/16375-78-3_b.png)
![Benzene,1-methyl-3-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/14100/14064-48-3.png)
![Benzene,1-methyl-3-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/14100/14064-48-3_b.png)
![2,4-Methano-1H-cycloprop[cd]indene,octahydro-](http://img.cochemist.com/ccimg/10600/10501-16-3.png)
![2,4-Methano-1H-cycloprop[cd]indene,octahydro-](http://img.cochemist.com/ccimg/10600/10501-16-3_b.png)
![4-[2-(4-NITROPHENYL)ETHENYL]PYRIDINE](http://img.cochemist.com/ccimg/7400/7372-12-5.png)
![4-[2-(4-NITROPHENYL)ETHENYL]PYRIDINE](http://img.cochemist.com/ccimg/7400/7372-12-5_b.png)
![Pyridine,4-[(1Z)-2-(4-chlorophenyl)ethenyl]-](http://img.cochemist.com/ccimg/5900/5847-63-2.png)
![Pyridine,4-[(1Z)-2-(4-chlorophenyl)ethenyl]-](http://img.cochemist.com/ccimg/5900/5847-63-2_b.png)
![(6aR,6bS,12bS,12cR)-6a,6b,12b,12c-tetrahydrocyclobuta[1,2-c:4,3-c']dichromene-6,7-dione](http://img.cochemist.com/ccimg/5300/5248-11-3.png)
![(6aR,6bS,12bS,12cR)-6a,6b,12b,12c-tetrahydrocyclobuta[1,2-c:4,3-c']dichromene-6,7-dione](http://img.cochemist.com/ccimg/5300/5248-11-3_b.png)
![PYRIDINE, 3-[(1E)-2-PHENYLETHENYL]-](http://img.cochemist.com/ccimg/5100/5097-91-6.png)
![PYRIDINE, 3-[(1E)-2-PHENYLETHENYL]-](http://img.cochemist.com/ccimg/5100/5097-91-6_b.png)
![Dibenzo[a,f]cyclopropa[cd]pentalene, 4b,8b,8c,8e-tetrahydro-](/data/chemimg/16200/2199-28-2.png)
![Dibenzo[a,f]cyclopropa[cd]pentalene, 4b,8b,8c,8e-tetrahydro-](/data/chemimg/16200/2199-28-2_b.png)
![2-[(Z)-2-phenylethenyl]pyridine](http://img.cochemist.com/ccimg/1600/1519-59-1.png)
![2-[(Z)-2-phenylethenyl]pyridine](http://img.cochemist.com/ccimg/1600/1519-59-1_b.png)
![2-[(e)-2-phenylethenyl]pyridine](http://img.cochemist.com/ccimg/600/538-49-8.png)
![2-[(e)-2-phenylethenyl]pyridine](http://img.cochemist.com/ccimg/600/538-49-8_b.png)
![Benz[f]isoquinoline](http://img.cochemist.com/ccimg/300/229-67-4.png)
![Benz[f]isoquinoline](http://img.cochemist.com/ccimg/300/229-67-4_b.png)
![Naphth[1,2-h]isoquinoline](http://img.cochemist.com/ccimg/300/218-06-4.png)
![Naphth[1,2-h]isoquinoline](http://img.cochemist.com/ccimg/300/218-06-4_b.png)
![Dextroamphetamine sulfate [USAN]](http://img.cochemist.com/ccimg/100/51-63-8.png)
![Dextroamphetamine sulfate [USAN]](http://img.cochemist.com/ccimg/100/51-63-8_b.png)
![Benz[h]isoquinoline hydrochloride](http://img.cochemist.com/ccimg/868900/868838-97-5.png)
![Benz[h]isoquinoline hydrochloride](http://img.cochemist.com/ccimg/868900/868838-97-5_b.png)
![Heptacyclo[31.3.1.13,7.19,13.115,19.121,25.127,31]dotetraconta-1(37),3,5,7(42),9,11,13(41),15,17,19(40),21,23,25(39),27,29,31(38),33,35-octadecaene-5,11,17,23,29,35-hexasulfonic acid, 37,38,39,40,41,42-hexahydroxy-](/data/chemimg/103300/102088-39-1.png)
![Heptacyclo[31.3.1.13,7.19,13.115,19.121,25.127,31]dotetraconta-1(37),3,5,7(42),9,11,13(41),15,17,19(40),21,23,25(39),27,29,31(38),33,35-octadecaene-5,11,17,23,29,35-hexasulfonic acid, 37,38,39,40,41,42-hexahydroxy-](/data/chemimg/103300/102088-39-1_b.png)
![SPIRO[3H-DIAZIRINE-3,2'-TRICYCLO[3.3.1.13,7]DECAN]-5'-OL](http://img.cochemist.com/ccimg/90200/90125-35-2.png)
![SPIRO[3H-DIAZIRINE-3,2'-TRICYCLO[3.3.1.13,7]DECAN]-5'-OL](http://img.cochemist.com/ccimg/90200/90125-35-2_b.png)
![Pyridine, 4,4'-[(1R,2R,3S,4S)-3,4-diphenyl-1,2-cyclobutanediyl]bis-, rel-](http://img.cochemist.com/ccimg/62300/62210-12-2.png)
![Pyridine, 4,4'-[(1R,2R,3S,4S)-3,4-diphenyl-1,2-cyclobutanediyl]bis-, rel-](http://img.cochemist.com/ccimg/62300/62210-12-2_b.png)
![Pyridine,4-[(1E)-2-(4-methoxyphenyl)ethenyl]-](http://img.cochemist.com/ccimg/46800/46739-60-0.png)
![Pyridine,4-[(1E)-2-(4-methoxyphenyl)ethenyl]-](http://img.cochemist.com/ccimg/46800/46739-60-0_b.png)
![4-[2-(4-CHLOROPHENYL)ETHENYL]PYRIDINE](http://img.cochemist.com/ccimg/46500/46459-15-8.png)
![4-[2-(4-CHLOROPHENYL)ETHENYL]PYRIDINE](http://img.cochemist.com/ccimg/46500/46459-15-8_b.png)
![1-METHYL-2-[(Z)-2-(2-METHYLPHENYL)ETHENYL]BENZENE](http://img.cochemist.com/ccimg/36900/36888-18-3.png)
![1-METHYL-2-[(Z)-2-(2-METHYLPHENYL)ETHENYL]BENZENE](http://img.cochemist.com/ccimg/36900/36888-18-3_b.png)
![Pyridine, 4-[(1Z)-2-phenylethenyl]-, hydrochloride](http://img.cochemist.com/ccimg/19200/19149-60-1.png)
![Pyridine, 4-[(1Z)-2-phenylethenyl]-, hydrochloride](http://img.cochemist.com/ccimg/19200/19149-60-1_b.png)
![6B,6C,12B,12C-TETRAHYDROCYCLOBUTA[1,2-A_3,4-A']DIACENAPHTHYLENE](http://img.cochemist.com/ccimg/7300/7259-03-2.png)
![6B,6C,12B,12C-TETRAHYDROCYCLOBUTA[1,2-A_3,4-A']DIACENAPHTHYLENE](http://img.cochemist.com/ccimg/7300/7259-03-2_b.png)
![Pyridine, 4-[(1Z)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/5100/5097-92-7.png)
![Pyridine, 4-[(1Z)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/5100/5097-92-7_b.png)
![BENZO[F]QUINOLINE, HYDROCHLORIDE](http://img.cochemist.com/ccimg/700/605-86-7.png)
![BENZO[F]QUINOLINE, HYDROCHLORIDE](http://img.cochemist.com/ccimg/700/605-86-7_b.png)
![Nonacyclo[43.3.1.13,7.19,13.115,19.121,25.127,31.133,37.139,43]hexapentaconta-1(49),3,5,7(56),9,11,13(55),15,17,19(54),21,23,25(53),27,29,31(52),33,35,37(51),39,41,43(50),45,47-tetracosaene-5,11,17,23,29,35,41,47-octasulfonic acid, 49,50,51,52,53,54,55,56-octahydroxy-](/data/chemimg/103300/137407-62-6.png)
![Nonacyclo[43.3.1.13,7.19,13.115,19.121,25.127,31.133,37.139,43]hexapentaconta-1(49),3,5,7(56),9,11,13(55),15,17,19(54),21,23,25(53),27,29,31(52),33,35,37(51),39,41,43(50),45,47-tetracosaene-5,11,17,23,29,35,41,47-octasulfonic acid, 49,50,51,52,53,54,55,56-octahydroxy-](/data/chemimg/103300/137407-62-6_b.png)
![[4-(ETHOXYMETHYL)PHENYL]-PHENYLMETHANONE](http://img.cochemist.com/ccimg/71900/71850-73-2.png)
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