Co-reporter:Ying Wang, Arnon Olankitwanit, Suchada Rajca, and Andrzej Rajca
Journal of the American Chemical Society May 31, 2017 Volume 139(Issue 21) pp:7144-7144
Publication Date(Web):May 17, 2017
DOI:10.1021/jacs.7b02692
We report a large kinetic isotope effect at 298 K, kH/kD ≈ 150, associated with an intramolecular 1,5-hydrogen atom transfer (1,5-HAT) in the decay of a PEGylated carbazyl (aminyl) radical in solution. The experimental observations surprisingly combine the hallmarks of tunneling, including large KIEs and unusual activation parameters, with linear Arrhenius and Eyring plots over an exceptionally wide temperature range of 116 K.
Co-reporter:Ying Wang, Suchada Rajca, and Andrzej Rajca
The Journal of Organic Chemistry July 21, 2017 Volume 82(Issue 14) pp:7512-7512
Publication Date(Web):June 27, 2017
DOI:10.1021/acs.joc.7b01212
We report the synthesis and kinetic study of PEGylated, water-soluble aminyl radical 2. The radical possesses four mPEG-3 groups replacing four methyl groups in the tert-butyl groups at the 3- and 6-positions of 1,3,6,8-tetra-tert-butyl carbazyl (TTBC). This structure is designed to mitigate the rapid decomposition of the radical via intramolecular 1,5-hydrogen atom transfer (1,5-HAT) that was observed in its constitutional isomer 1-H with four mPEG-3 groups in the vicinity of the nitrogen-centered radical (1- and 8-positions of TTBC). In dry, degassed acetone at 295 K, the radical 2 has a half-life, τ1/2 = 49 h (ΔH‡ = 17.9 ± 0.8 kcal mol–1), which is 3 orders of magnitude longer than that for 1-H, which decays via 1,5-HAT (τ1/2 = 48 s, ΔH‡ = 10.0 ± 0.3 kcal mol–1). Aminyl radical 2 aggregates at ambient conditions in water and has a half-life, τ1/2 = 2 h.
Co-reporter:Shengdian Huang, Joseph T. Paletta, Hanan Elajaili, Kirby Huber, Maren Pink, Suchada Rajca, Gareth R. Eaton, Sandra S. Eaton, and Andrzej Rajca
The Journal of Organic Chemistry 2017 Volume 82(Issue 3) pp:
Publication Date(Web):December 29, 2016
DOI:10.1021/acs.joc.6b02737
We report the design, synthesis, and electron spin relaxation properties of hydrophilic tetracarboxylate ester pyrroline nitroxides 1 and 2, which serve as models in the search for new spin labels for DEER distance measurement at room temperature. The nitroxides are designed to have the methyl groups further away from the N–O spin site to decrease the inequivalent couplings of the unpaired electron to the methyl protons that shorten Tm at T > 70 K in currently used labels. The key step in the synthesis of 1 and 2 is the reaction of the dianion of pyrrole-1,2,5-tricarboxylic acid tert-butyl ester dimethyl ester with electrophiles such as methyl chloroformate and methyl bromoacetate. Structures of 1 and 2 are confirmed by X-ray crystallography. Studies of electron spin relaxation rates in rigid trehalose/sucrose matrices reveal approximately temperature independent values of 1/Tm for 1 and 2 up to about 160 K and modest temperature dependence up to 295 K, demonstrating that increasing the distance between the nitroxide moiety and methyl groups is effective in lengthening Tm at T > 70 K.
Co-reporter:Sheng Zhang, Xinming Liu, Chunli Li, Lu Li, Jinsheng Song, Jianwu Shi, Martha Morton, Suchada Rajca, Andrzej Rajca, and Hua Wang
Journal of the American Chemical Society 2016 Volume 138(Issue 31) pp:10002-10010
Publication Date(Web):July 21, 2016
DOI:10.1021/jacs.6b05709
We demonstrate facile and efficient construction of conjugated double helical ladder oligomers from the saddle-shaped cyclooctatetrathiophene (COTh) building blocks. The key step involves deprotonation of tetra[3,4]thienylene (β,β-COTh) with n-BuLi which displays remarkably high ipsilateral selectivity. Three racemic double helical ladder oligomers, rac-DH-1, rac-DH-2, and rac-DH-3, containing two, three, and five COTh annelated moieties are efficiently synthesized by diastereoselective coupling of the racemic precursors. The X-ray crystallographic studies of rac-DH-1, rac-DH-2 and rac-DH-3 unambiguously revealed that each double helical scaffold has two single helices intertwined with each other via the C–C single bonds. Following removal of TMS groups, double helical ladder oligomer rac-DH-1-D had sufficient solubility to be resolved via chiral HPLC, thus enabling determination of its chirooptical properties such as CD spectra and optical rotation. (+)-DH-1-D has a large barrier for racemization, with lower limit of ΔG‡ > 48 kcal mol–1, which may be compared to DFT-computed barrier of 51 kcal mol–1. The enantiomers of DH-1-D show 1 order of magnitude stronger chirooptical properties than the carbon–sulfur [7]helicene, as determined by the anisotropy factor g = Δε/ε = −0.039, based on Δεmax = −11 and ε = 2.8 × 102 L mol–1 cm–1 in cyclohexane at 327 nm.
Co-reporter:Ying Wang; Hui Zhang; Maren Pink; Arnon Olankitwanit; Suchada Rajca
Journal of the American Chemical Society 2016 Volume 138(Issue 23) pp:7298-7304
Publication Date(Web):May 24, 2016
DOI:10.1021/jacs.6b01498
We report a relatively persistent, open-shell aza-thia[7]helicene with cross-conjugated electron-rich π-system. The singly occupied molecular orbital (SOMO) energy levels of both radical cation and neutral radical of the [7]helicene are below the highest occupied molecular orbital (HOMO) energy levels, thereby violating the Aufbau principle. The aza-thia[7]helicene is prepared from β-hexathiophene by a three-step one-pot reaction, in which the pyrrole ring is constructed by two consecutive C–N bond formations. Chemical oxidation converts the helicene to its radical cation, while in the presence of base (Cs2CO3), the oxidation gives neutral aminyl radical, likely via proton dissociation from the aminium radical cation with a low pKa. Reaction of the aza-thia[7]helicene with NaH provides the corresponding anion, which shows characteristic cyclic voltammetry wave at anodic peak potential Epa ≈ +0.2 V. Chemical oxidation of the anion with ferrocenium hexafluorophosphate at room temperature gives persistent neutral aminyl radical. Structure of the aza-thia[7]helicene is supported by NMR, IR, X-ray crystallography, and cyclic voltammetry. The radical cation and neutral radical are characterized by EPR and UV–vis-NIR spectroscopies. DFT computations of the radical cation and neutral radical predict the SOMO–HOMO energy level inversion, which is supported experimentally by electrochemical data for the radical cation.
Co-reporter:Nolan M. Gallagher; Jackson J. Bauer; Maren Pink; Suchada Rajca
Journal of the American Chemical Society 2016 Volume 138(Issue 30) pp:9377-9380
Publication Date(Web):July 19, 2016
DOI:10.1021/jacs.6b05080
Triplet ground-state organic molecules are interesting with respect to several emerging technologies but typically exhibit limited stability. We report two organic diradicals, one of which possesses a triplet ground state (2J/kB = 234 ± 36 K) and robust stability at elevated temperatures. We are able to sublime this high-spin diradical under high vacuum at 140 °C with no significant decomposition.
Co-reporter:F. Ciccullo, N. M. Gallagher, O. Geladari, T. Chassé, A. Rajca, and M. B. Casu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 3) pp:1805
Publication Date(Web):January 4, 2016
DOI:10.1021/acsami.5b09693
Organic radicals are fascinating materials because of their unique properties, which make them suitable for a variety of applications. Their synthesis may be challenging, and big efforts have focused on chemical stability. However, introducing a new material in electronics not only requires chemically stable molecules but also stable monolayers and thin films in view of their use in devices. In this work, we have investigated the thin films of a derivative of the Blatter radical that was synthesized bearing in mind the thermodynamic factors that govern thin film stability. We have proved our concept by investigating the electronic structure, the paramagnetic character, and stability of the obtained films under UHV and ambient conditions by in situ X-ray photoelectron spectroscopy, ex situ atomic force microscopy, and electron paramagnetic resonance spectroscopy.Keywords: organic electronics; organic magnetism; organic radicals; spinterface; thin film processes
Co-reporter:Arnon Olankitwanit, Suchada Rajca, and Andrzej Rajca
The Journal of Organic Chemistry 2015 Volume 80(Issue 10) pp:5035-5044
Publication Date(Web):April 22, 2015
DOI:10.1021/acs.joc.5b00421
Aminyl diradical 3, a derivative of aza-m-xylylene, is expected to be more stable than diradical 1, due to increased steric protection of the radicals by additional methyl groups in the pendant group. Here we report synthesis and characterization of diradical 3. The structure of diamine precursor 6 is characterized by high-field 1H NMR spectroscopy in which the two diastereomers (meso and ± pair) are distinguishable. In addition, correlation between the DFT-calculated and experimental 1H and 13C NMR chemical shifts provides evidence in support of the diamine structure. Electrochemistry of the diamine is carried out to explore redox properties and stability of the corresponding aminium diradical dications. The ground state and ΔEST for 3 are established by statistical analyses of mean χT determined by EPR spectroscopy. Decay kinetics of aminyl diradical 3 indicates that the decay of 3 is faster than that of 1, possibly due to intramolecular hydrogen atom abstraction from benzylic methyl groups in 3, followed by intermolecular hydrogen atom abstraction from 2-MeTHF solvent.
Co-reporter:Nolan M. Gallagher, Arnon Olankitwanit, and Andrzej Rajca
The Journal of Organic Chemistry 2015 Volume 80(Issue 3) pp:1291-1298
Publication Date(Web):January 9, 2015
DOI:10.1021/jo502505r
Organic molecules with high-spin ground states, besides being fundamentally interesting, possess numerous potential applications in diverse fields such organic magnetism, MRI contrast agents, and spintronics. Such molecules, once thought to exist only as highly reactive intermediates, can be rationally designed to have adequate stability for organic synthesis and characterization. This Synopsis provides an overview of the factors that lead to high-spin ground states as well as recent progress in the design and synthesis of high-spin organic molecules.
Co-reporter:Arnon Olankitwanit ; Maren Pink ; Suchada Rajca
Journal of the American Chemical Society 2014 Volume 136(Issue 40) pp:14277-14288
Publication Date(Web):September 12, 2014
DOI:10.1021/ja508119d
We describe synthesis and characterization of a derivative of aza-m-xylylene, diradical 2, that is persistent in solution at room temperature with the half-life measured in minutes (∼80–250 s) and in which the triplet ground state is below the lowest singlet state by >10 kcal mol–1. The triplet ground states and ΔEST of 2 in glassy solvent matrix are determined by a new approach based on statistical analyses of their EPR spectra. Characterization and analysis of the analogous diradical 1 are carried out for comparison. Statistical analyses of their EPR spectra reliably provide improved lower bounds for ΔEST (from >0.4 to >0.6 kcal mol–1) and are compatible with a wide range of relative contents of diradical vs monoradical, including samples in which the diradical and monoradical are minor and major components, respectively. This demonstrates a new powerful method for the determination of the triplet ground states and ΔEST applicable to moderately pure diradicals in matrices.
Co-reporter:Ying Wang, Joseph T. Paletta, Kathleen Berg, Erin Reinhart, Suchada Rajca, and Andrzej Rajca
Organic Letters 2014 Volume 16(Issue 20) pp:5298-5300
Publication Date(Web):September 16, 2014
DOI:10.1021/ol502449r
A series of unnatural amino acids functionalized with sterically shielded pyrroline nitroxides were synthesized. Their reduction by ascorbate/glutathione indicates that l-cysteine functionalized with gem-diethylpyrroline nitroxide is reduced at the slowest rate and is comparable to that measured for the most resistant to reduction pyrroline and pyrrolidine nitroxides.
Co-reporter:Andrzej Rajca ; Arnon Olankitwanit ; Ying Wang ; Przemysław J. Boratyński ; Maren Pink ;Suchada Rajca
Journal of the American Chemical Society 2013 Volume 135(Issue 48) pp:18205-18215
Publication Date(Web):November 4, 2013
DOI:10.1021/ja409472f
Aminyl tetraradicals with planar tetraazanonacene backbones have quintet (S = 2) ground states and do not show any detectable thermal population of the low-spin excited states up to the highest temperature investigated (100 K) in the 2-methyltetrahydrofuran (2-MeTHF) matrix. This indicates that the nearest electronic excited state (triplet) is at least ∼0.3 kcal mol–1 higher in energy, that is, the triplet–quintet energy gap, ΔETQ > 0.3 kcal mol–1, which is consistent with the broken-symmetry-DFT-computed ΔETQ of about 5 kcal mol–1. In concentrated (ca. 1–10 mM) solutions of tetraradical 4 in 2-MeTHF at 133 K, a fraction of tetraradicals form a dimer (association constant, Kassoc ≈ 60 M–1), with a weak, antiferromagnetic exchange coupling, J/k ≈ −0.1 K ∼ 0.2 cal mol–1, between the S = 2 tetraradicals. This weak intradimer exchange coupling is expected for two tetraradicals at the distance of about 6 Å. The most sterically shielded tetraradical 5 in 2-MeTHF has a half-life of 1 h at room temperature; the product of its decay is the corresponding tetraamine, suggesting that the hydrogen atom abstraction from the solvent is primarily responsible for the decomposition of the tetraradical.
Co-reporter:Andrzej Rajca ; Ying Wang ; Michael Boska ; Joseph T. Paletta ; Arnon Olankitwanit ; Michael A. Swanson ; Deborah G. Mitchell ; Sandra S. Eaton ; Gareth R. Eaton ;Suchada Rajca
Journal of the American Chemical Society 2012 Volume 134(Issue 38) pp:15724-15727
Publication Date(Web):September 13, 2012
DOI:10.1021/ja3079829
We report a molecular design that provides an intravenously injectable organic radical contrast agent (ORCA) for which the molecular 1H water relaxivity (r1) is ca. 5 mM–1 s–1. The ORCA is based on spirocyclohexyl nitroxide radicals and poly(ethylene glycol) chains conjugated to a fourth-generation polypropylenimine dendrimer scaffold. The metal-free ORCA has a long shelf life and provides selectively enhanced magnetic resonance imaging in mice for over 1 h.
Co-reporter:Joseph T. Paletta, Maren Pink, Bridget Foley, Suchada Rajca, and Andrzej Rajca
Organic Letters 2012 Volume 14(Issue 20) pp:5322-5325
Publication Date(Web):October 10, 2012
DOI:10.1021/ol302506f
A series of sterically shielded pyrrolidine nitroxides were synthesized, and their reduction by ascorbate (vitamin C) indicate that nitroxide 3, a tetraethyl derivative of 3-carboxy-PROXYL, is reduced at the slowest rate among known nitroxides, i.e., at a 60-fold slower rate than that for 3-carboxy-PROXYL.
Co-reporter:Andrzej Rajca, Przemysław J. Boratyński, Arnon Olankitwanit, Kouichi Shiraishi, Maren Pink, and Suchada Rajca
The Journal of Organic Chemistry 2012 Volume 77(Issue 5) pp:2107-2120
Publication Date(Web):February 13, 2012
DOI:10.1021/jo2025948
We describe the synthesis and electronic properties of ladder oligomers of poly(m-aniline) that may be considered as derivatives of azaacenes with cross-conjugated π-systems. Syntheses of ladder oligo(m-aniline)s with 9 and 13 collinearly fused six-membered rings employed Pd-catalyzed aminations and Friedel–Crafts-based ring closures. Structures were confirmed by either X-ray crystallography or correlations between DFT-computed and experimental spectroscopic data such as 1H, 13C, and 15N NMR chemical shifts and electronic absorption spectra. All compounds have planar “azaacene” moieties. The experimental band gaps Eg ≈ 3.5–3.65 eV, determined by the UV–vis absorption onsets, were in agreement with the TD-DFT-computed vertical excitation energies to the S1 state. Fluorescence quantum yields of up to 20% were found. Electrochemically estimated HOMO energies of −4.8 eV suggested propensity for a facile one-electron oxidation and just sufficient environmental stability toward oxygen (O2). For two oligomers with “tetraazanonacene” moieties, potentials of E4+/3+ ≈ 1.6–1.7 V vs SCE were determined for four-electron oxidation to the corresponding tetraradical tetracations.
Co-reporter:Andrzej Rajca ; Arnon Olankitwanit ;Suchada Rajca
Journal of the American Chemical Society 2011 Volume 133(Issue 13) pp:4750-4753
Publication Date(Web):March 14, 2011
DOI:10.1021/ja200708b
Organic molecules with a strong preference for triplet ground states, in which the triplet state is below the lowest singlet state by ≥10 kcal/mol, are typically short-lived and mostly detected as reactive intermediates. We now report a triplet ground state derivative of aza-m-xylylene diradical with a large singlet−triplet energy gap (ΔEST) of ∼10 kcal/mol, which is comparable to ΔEST for the well-known reactive intermediate m-xylylene diradical. The aminyl diradical persists in solution at room temperature on the time scale of minutes.
Co-reporter:Arnon Olankitwanit, Velavan Kathirvelu, Suchada Rajca, Gareth R. Eaton, Sandra S. Eaton and Andrzej Rajca
Chemical Communications 2011 vol. 47(Issue 22) pp:6443-6445
Publication Date(Web):04 May 2011
DOI:10.1039/C1CC11172H
1,3-Alternate calix[4]arene with para-phenylene spacers connecting nitroxide monoradicals and high-spin (S = 1) diradicals provides tetraradical and octaradical scaffolds that possess conformations with slow electron spin relaxation rates (1/T1). Such scaffolds may facilitate tuning of relaxation rates that are more favorable for MRI or DNP applications.
Co-reporter:Andrzej Rajca, Kouichi Shiraishi, Przemysław J. Boratyński, Maren Pink, Makoto Miyasaka, and Suchada Rajca
The Journal of Organic Chemistry 2011 Volume 76(Issue 20) pp:8447-8457
Publication Date(Web):September 6, 2011
DOI:10.1021/jo2017923
Oxidation of diaryldiamine 2, a tetrahydrodiazapentacene derivative, provides diarylnitroxide diradical 1 accompanied by an intermediate nitroxide monoradical and a multitude of isolable diamagnetic products. DFT-computed tensors for EPR spectra and paramagnetic 1H NMR isotropic shifts for nitroxide diradical 1 show good agreement with the experimental EPR spectra in rigid matrices and paramagnetic 1H NMR spectra in solution, respectively. Examination of the diamagnetic products elucidates their formation via distinct pathways involving C–O bond-forming reactions, including Baeyer–Villiger-type oxidations. An unusual diiminoketone structure and two spirocyclic structures of the predominant diamagnetic products are confirmed by either X-ray crystallography or correlations between DFT-computed and experimental spectroscopic data such as 1H, 13C, and 15N NMR chemical shifts and electronic absorption spectra.
Co-reporter:Jerzy K. Zak ; Makoto Miyasaka ; Suchada Rajca ; Mieczyslaw Lapkowski
Journal of the American Chemical Society 2010 Volume 132(Issue 10) pp:3246-3247
Publication Date(Web):February 19, 2010
DOI:10.1021/ja910076n
The radical cation of carbon−sulfur [7]helicene is configurationally stable in solution at room temperature. In contrast to the radical cations of α-oligothiophenes, which form diamagnetic π-dimers at low temperature, the radical cation of this helical, cross-conjugated β-oligothiophene shows a low propensity toward dimerization.
Co-reporter:Makoto Miyasaka, Maren Pink, Suchada Rajca and Andrzej Rajca
Organic Letters 2010 Volume 12(Issue 14) pp:3230-3233
Publication Date(Web):June 15, 2010
DOI:10.1021/ol1011696
Linear oligothiophenes, containing annelated dithieno[2,3-b:3′,2′-d]thiophene units, undergo unexpected spirocyclizations upon treatment with trifluoroacetic acid. The resultant spiro oligothiophenes possess novel structures in which the spiro or dispiro skeleton is within an all-thiophene/dihydrothiophene framework. Racemic dispiro octathiophene is obtained with high diastereoselectivity and in high yield.
Co-reporter:Andrzej Rajca ;Suchada Rajca Dr.
Angewandte Chemie International Edition 2010 Volume 49( Issue 4) pp:672-674
Publication Date(Web):
DOI:10.1002/anie.200905421
Co-reporter:Przemys&x142;awJ. Boraty&x144;ski Dr.;Maren Pink Dr.;Suchada Rajca Dr. Dr.
Angewandte Chemie International Edition 2010 Volume 49( Issue 32) pp:5459-5462
Publication Date(Web):
DOI:10.1002/anie.201002811
Co-reporter:Andrzej Rajca ;Velavan Kathirvelu Dr.;SipK. Roy Dr.;Maren Pink Dr.;Suchada Rajca Dr.;Santanu Sarkar;SraS. Eaton ;GarethR. Eaton
Chemistry - A European Journal 2010 Volume 16( Issue 19) pp:5778-5782
Publication Date(Web):
DOI:10.1002/chem.200903102
Abstract
Site-directed spin labeling and EPR spectroscopy offer accurate, sensitive tools for the characterization of structure and function of macromolecules and their assemblies. A new rigid spin label, spirocyclohexyl nitroxide α-amino acid and its N-(9-fluorenylmethoxycarbonyl) derivative, have been synthesized, which exhibit slow enough spin-echo dephasing to permit accurate distance measurements by pulsed EPR spectroscopy at temperatures up to 125 K in 1:1 water/glycerol and at higher temperatures in matrices with higher glass transition temperatures. Distance measurements in the liquid nitrogen temperature range are less expensive than those that require liquid helium, which will greatly facilitate applications of pulsed EPR spectroscopy to the study of structure and conformation of peptides and proteins.
Co-reporter:Andrzej Rajca ;Suchada Rajca Dr.
Angewandte Chemie 2010 Volume 122( Issue 4) pp:683-685
Publication Date(Web):
DOI:10.1002/ange.200905421
Co-reporter:Przemys&x142;awJ. Boraty&x144;ski Dr.;Maren Pink Dr.;Suchada Rajca Dr. Dr.
Angewandte Chemie 2010 Volume 122( Issue 32) pp:5591-5594
Publication Date(Web):
DOI:10.1002/ange.201002811
Co-reporter:Andrzej Rajca, Kouichi Shiraishi and Suchada Rajca
Chemical Communications 2009 (Issue 29) pp:4372-4374
Publication Date(Web):25 Jun 2009
DOI:10.1039/B909741D
Nitroxide diradical 2, the first isolated diarylnitroxide diradical, is stable in the solid state at room temperature and it possesses triplet ground state with strong ferromagnetic coupling.
Co-reporter:Makoto Miyasaka Dr.;Maren Pink Dr.;Suchada Rajca Dr.
Angewandte Chemie 2009 Volume 121( Issue 32) pp:6068-6071
Publication Date(Web):
DOI:10.1002/ange.200901349
Co-reporter:Makoto Miyasaka Dr.;Maren Pink Dr.;Suchada Rajca Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 32) pp:5954-5957
Publication Date(Web):
DOI:10.1002/anie.200901349
Co-reporter:Gaëlle Spagnol, Kouichi Shiraishi, Suchada Rajca and Andrzej Rajca
Chemical Communications 2005 (Issue 40) pp:5047-5049
Publication Date(Web):16 Sep 2005
DOI:10.1039/B508094K
The synthesis and magnetic characterization of pegylated bis(aminoxyl) diradical with an S
= 1 ground state are presented, revealing water-induced changes in the molecular conformation and magnetic properties.
Co-reporter:Makoto Miyasaka Dr. ;Maren Pink Dr.;Suchada Rajca Dr.
Chemistry - A European Journal 2004 Volume 10(Issue 24) pp:
Publication Date(Web):11 NOV 2004
DOI:10.1002/chem.200400635
Synthesis of thiophene-based [7]helicenes, which are functionalized for both design of organic chiral glasses with strong chiroptical properties and for further homologation to higher [n]helicenes, is reported. The key synthetic transformations are kinetic resolution of the intermediate diketone and the annelation step forming the center benzene ring by means of an intramolecular McMurry reaction. Based upon X-ray crystallographic determinations of the absolute configurations for (+)-enantiomers of the diketone and the [7]helicene, stereochemical correlation between the (R) axial chirality of the diketone and the (M) helical chirality of the [7]helicene is established. One such enantiopure trimethylsilyl-substituted [7]helicene possesses enchanced chiroptical properties and forms a chiral molecular glass.
Co-reporter:Andrzej Rajca
Chemistry - A European Journal 2002 Volume 8(Issue 21) pp:
Publication Date(Web):22 OCT 2002
DOI:10.1002/1521-3765(20021104)8:21<4834::AID-CHEM4834>3.0.CO;2-E
This concept paper outlines the design of the first π-conjugated organic polymer with magnetic ordering. This rational, “bottom-up” macromolecular design is based on synthesis and study of polyarylmethyl polyradicals with increasing number of exchange-coupled unpaired electron spins. The prospects for attaining organic polymer magnets with stability at ambient temperature and/or higher magnetic ordering temperatures will be discussed.
Co-reporter:Andrzej Rajca, Suchada Rajca and Jirawat Wongsriratanakul
Chemical Communications 2000 (Issue 12) pp:1021-1022
Publication Date(Web):23 May 2000
DOI:10.1039/B001273O
The novel cyclophane diradical 1 possesses a singlet ground
state with a singlet–triplet energy gap
(ΔEST) of −0.20 and −0.24 kcal
mol−1, as measured with SQUID magnetometry and EPR
spectroscopy, respectively. This large
ΔEST may in part be associated with the
two parallel 3,3′-biphenyl exchange coupling pathways (ECPs).
Co-reporter:Andrzej Rajca ;Hua Wang Dr.;Maren Pink Dr.;Suchada Rajca Dr.
Angewandte Chemie 2000 Volume 112(Issue 24) pp:
Publication Date(Web):15 DEC 2000
DOI:10.1002/1521-3757(20001215)112:24<4655::AID-ANGE4655>3.0.CO;2-X
Durch eine iterative Route wurde das Oligothiophen 1, ein Kohlenstoff-Schwefel(C2S)-Helicen-Fragment, hergestellt. Kennzeichnend für die Eigenschaften von 1 sind die kreuzkonjugierten anellierten Thiophenringe.
Co-reporter:Makoto Miyasaka ; Maren Pink ; Arnon Olankitwanit ; Suchada Rajca
Organic Letters () pp:
Publication Date(Web):May 31, 2012
DOI:10.1021/ol3011437
Asymmetric synthesis of (−)-[9]helicene, as well as preparation of its lower homologues, completes the series of carbon–sulfur [5]-, [7]-, [9]-, and [11]helicenes. Spectroscopic and electrochemical studies of this series provide an absorption onset-based band gap, Eg = 3.40 eV, for a cross-conjugated (C2S)n helix; this value may be compared to Eg = 3.59 eV obtained from TD-DFT computed excitation energies for a series of dimethyl-substituted [n]helicenes (n ≤ 31).
Co-reporter:Andrzej Rajca, Kouichi Shiraishi and Suchada Rajca
Chemical Communications 2009(Issue 29) pp:NaN4374-4374
Publication Date(Web):2009/06/25
DOI:10.1039/B909741D
Nitroxide diradical 2, the first isolated diarylnitroxide diradical, is stable in the solid state at room temperature and it possesses triplet ground state with strong ferromagnetic coupling.
Co-reporter:Arnon Olankitwanit, Velavan Kathirvelu, Suchada Rajca, Gareth R. Eaton, Sandra S. Eaton and Andrzej Rajca
Chemical Communications 2011 - vol. 47(Issue 22) pp:NaN6445-6445
Publication Date(Web):2011/05/04
DOI:10.1039/C1CC11172H
1,3-Alternate calix[4]arene with para-phenylene spacers connecting nitroxide monoradicals and high-spin (S = 1) diradicals provides tetraradical and octaradical scaffolds that possess conformations with slow electron spin relaxation rates (1/T1). Such scaffolds may facilitate tuning of relaxation rates that are more favorable for MRI or DNP applications.
![7-Azadispiro[5.1.5.3]hexadec-7-yloxy, 15-oxo-](http://img.cochemist.com/ccimg/35900/35814-35-8.png)
![7-Azadispiro[5.1.5.3]hexadec-7-yloxy, 15-oxo-](http://img.cochemist.com/ccimg/35900/35814-35-8_b.png)
