A series of new [20]dioxahomoporphyrins have been synthesized by [2+2] condensation of (but-2-ene-2,3-diyldifuran-2,5-diyl)bis(p-methoxyphenylmethanol) with appropriate meso-aryldipyrromethanes under mild acid-catalyzed conditions. The X-ray structure determined for one of the dioxahomoporphyrins revealed that the macrocycle is significantly distorted and the two furan rings are completely out-of-plane from the mean plane. The [20]dioxahomoporphyrin macrocycles are stable and non-aromatic, and have been characterized in detail by HRMS, 1D and 2D NMR spectroscopy, UV/Vis spectrophotometry and electrochemical techniques. The iodo-functionalized [20]dioxahomoporphyrin was used to synthesize a covalently linked diphenylethyne-bridged [20]dioxahomoporphyrin–porphyrin dyad by coupling with an ethynyl-functionalized porphyrin under mild copper-free Pd⁰ catalytic conditions. The metallation of the porphyrin macrocycle of the [20]dioxahomoporphyrin–porphyrin dyad was carried out by treating the dyad with the appropriate metal salt under standard conditions and the resulting [20]dioxahomoporphyrin–metalloporphyrin dyads were characterized by various spectral and electrochemical techniques. The results of the studies indicated that in the dyads the dioxahomoporphyrin and porphyrin/metalloporphyrin units interact weakly and retain their individual features.

Smaragdyrin, a class of expanded porphyrin macrocycles, upon treatment with meta-chloroperoxybenzoic acid (mCPBA) underwent oxidative ring opening to form an unprecedented linear pentaheterocyclic compound. The linear pentaheterocyclic compound was freely soluble in common organic solvents and characterized in detail by HRMS, 1D and 2D NMR spectroscopy, and X-ray crystallography. Our preliminary studies indicated that the linear pentaheterocyclic compound can specifically sense anions such as H₂PO₄⁻ and CN⁻ ions, which was corroborated by absorption and fluorescence studies.

A series of fluorescent B^III complexes of meso-triaryl-substituted 25-oxasmaragdyrins containing axial silyloxy groups were prepared in 80–85 % yields by treating B(OH)₂ complexes of meso-triaryl 25-oxasmaragdyrins with different alkyl/aryl chlorosilanes in toluene in the presence of base at reflux temperature followed by simple column chromatographic purification. The eight axially silyloxy-substituted B^III complexes of smaragdyrins were freely soluble in common organic solvents and were characterized by HRMS, 1D and 2D NMR, absorption, fluorescence and electrochemical studies, as well as by X-ray crystallography in the case of one of the complexes. The crystal structure revealed that the smaragdyrin macrocycle is almost planar and that the –OSiMe₃ groups on B^III are oriented in the up and down directions relative to the macrocycle. The absorption studies indicated that the axially silyloxy-substituted B^III smaragdyrins are strongly absorbing in the 710–440 nm region with absorption coefficients higher than those of B(OH)₂-smaragdyrin complexes. The silylation of –OH groups at the B^III centre in the B^III smaragdyrin complex results in five- to sixfold enhancements in the fluorescence quantum yields and in longer singlet state lifetimes. Thus, the axial silyloxy B^III complexes are strongly fluorescent with quantum yields in the 0.65–0.78 range and singlet state lifetimes in the 4.3–4.9 ns range. The complexes are highly stable under redox conditions and each exhibit two reversible oxidations and one reversible reduction.

Our successful synthesis of nonaromatic 24π core-modified pentaphyrins containing six meso carbons is reported. The pentaphyrins were prepared by [3+2] condensation of butane-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with different meso-aryl tripyrromethanes under mild acid-catalyzed conditions. By using this method, we obtained two stable, core-modified pentaphyrins containing six meso carbons in acceptable yields. The pentaphyrins were characterized by HR-MS, 1D, 2D NMR, absorption and electrochemical techniques, and also by X-ray crystallography for one of the pentaphyrin macrocycles. The crystal structure revealed that the macrocycle is almost planar and one of the thiophene rings, which is positioned opposite to the ethene bridged meso-carbons, is inverted. Our studies revealed that the macrocycles in their protonated form have specific sensing ability for CH₃COO⁻ ions.

Cyclotriphosphazene and cyclotetraphosphazene appended with six and eight sapphyrin units, respectively, were prepared by treating N₃P₃Cl₆ and N₄P₄Cl₈ with the appropriate equivalents of 5,10,15-tri(p-tolyl)-20-(4-hydroxyphenyl)-25,27,29-trithiasapphyrin in tetrahydrofuran (THF) in the presence of Cs₂CO₃ at temperatures of 0 to 60 °C for 8–12 h. The two multi-expanded porphyrin assemblies were soluble in common organic solvents, and their identities were confirmed by their corresponding molecular ion peak in the MALDI-TOF mass spectra. 1D and 2D NMR spectroscopic techniques were used to deduce the molecular structures of the mult-expanded porphyrin assemblies. Absorption spectral studies showed that the band positions of the multisapphyrin assemblies were similar to that of the monomeric sapphyrin, but the extinction coefficients were three- to fourfold higher than that of the monomeric sapphyrin. The multisapphyrin assemblies are not very stable under redox conditions.

Unprecedented examples of smaragdyrin macrocycles containing seven membered heterocyclic rings were synthesized under simple reaction conditions in high yields. The heterocycle formed inside smaragdyrin macrocycle is rare example of heterocycle containing five different atoms, such as B, C, N, O, and P atoms. The mixed B^III and P^V complexes of smaragdyrin macrocycles showed new structural, spectral, and electrochemical properties.

Novel boron-dipyrromethene (BODIPY)-bridged 22-oxacorrole dyads, using meso-pyrrolyl 22-oxacorrole as a key synthon, have been synthesized. The reactivity of the meso-pyrrolyl group of 22-oxacorrole was exploited to synthesize the first examples of BODIPY-bridged 22-oxacorrole dyads in ≈40 % yield. The dyads are stable and exhibited interesting spectral and electrochemical properties.

We synthesized five N-methyl-meso-tetraaryl-21-thiaporphyrins in 55–60 % yield by treating the appropriate meso-tetraaryl-21-thiaporphyrin with CH₃I. The N-methyl-21-thiaporphyrins were characterized by HRMS, 1D and 2D NMR spectroscopy, absorption spectroscopy, fluorescence spectroscopy, and electrochemical techniques, and the structure of one of the compounds was obtained by X-ray crystallography. 1D and 2D NMR spectroscopy were used to identify all of the resonances observed in the ¹H NMR spectra of the N-methyl-21-thiaporphyrins. NMR studies indicated that the methylation occurred at the pyrrole ring that is opposite to the thiophene ring. In the ¹H NMR spectra, the methylation resulted in significant upfield shifts of the pyrrole and thiophene protons; the maximum shifts were noted for the protons of the N-methylated pyrrole ring of the N-methyl-21-thiaporphyrins. The X-ray structure of one of the N-methyl-21-thiaporphyrins revealed significant deviation of the N-methylated pyrrole ring from the reference plane defined by the four meso carbon atoms, and the porphyrin ring is strongly distorted compared to the 21-thiaporphyrin ring. The absorption studies revealed that the N-methyl-21-thiaporphyrins showed four Q bands and one strong Soret band, which were bathochromically shifted compared to those of the 21-thiaporphyrins. The electrochemical studies on the N-methyl-21-thiaporphyrins indicated that the oxidation potentials became less positive and there were negligible shifts in the reduction potentials; the HOMO–LUMO energy gap decreased compared with that of the 21-thiaporphyrins. The N-methyl-21-thiaporphyrins are weakly fluorescent with low quantum yields and singlet-state lifetimes. The spectral and electrochemical studies indicated that N-methylation of the pyrrole ring of 21-thiaporphyrins significantly alters the electronic properties of the 21-thiaporphyrin macrocycle.

A series of sterically crowded, mixed hexasubstituted BODIPYs containing two different types of substituents on the pyrrole carbons have been synthesized in high yields by a stepwise approach. The mixed BODIPYs were synthesized by bromination of BODIPYs followed by coupling with appropriate boronic acids under Suzuki coupling conditions. This approach has allowed the introduction of two different types of methyl/aryl substituents at the designated positions of the BODIPY core. All the hexasubstituted BODIPYs are readily soluble in common organic solvents and have been characterized by various spectral and electrochemical techniques. The spectral studies indicated that the presence of mixed methyl/aryl substituents on the BODIPY core significantly alters the electronic properties, and the electrochemical studies revealed that the BODIPYs are stable under redox conditions.

A simple route was developed for the synthesis of 9,10,19,20-tetraarylporphycenes by combining both McMurry and oxidative synthetic strategies and using readily available precursors. The desired 5,6-diaryldipyrroethenes, which were prepared in multigram quantities over two steps, were used to prepare 9,10,19,20-tetraarylporphycenes under mild acid-catalyzed conditions. As 5,6-diaryldipyrroethene precursors can easily be prepared in multigram quantities, this method is useful for the preparation of meso-tetrarylporphycenes that contain different aryl substituents. The molecular structures of these macrocycles were determined by HRMS analysis as well as 1D and 2D NMR studies. The tetraarylporphycenes exhibited a strong Soret band at approximately 380 nm and three Q bands in the region of 580–655 nm. The tetraarylprophycenes are reasonably fluorescent and stable under redox conditions.

A simple synthetic route was developed for the decomplexation of F-BODIPYs (fluorine-substituted boron–dipyrromethenes) to afford dipyrrins in high yields. This was achieved by treating the F-BODIPYs with different Lewis acids such as ZrCl₄, TiCl₄, AlCl₃, Sc(OTf)₃, or SnCl₄ in CH₃CN/CH₃OH under refluxing conditions. This synthetic strategy was efficient for different types of F-BODIPYs such as meso-aryl-substituted BODIPYs, 3-pyrrolyl BODIPYs, functionalized 3-pyrrolyl BODIPYs, π-extended pyrrolyl BODIPYs, sterically crowded BODIPYs, and the BF₂ complex of 25-oxasmaragdyrin.

An alternate synthetic route was developed for tetraaryl 27-thiasapphyrins by condensation of meso-aryl dipyrromethanes with 2,5-bis(p-tolylhydroxymethyl)thiophene under acid-catalyzed conditions. Previously, 27-thiasapphyrins have been prepared by a multistep synthesis using 2,2′-bipyrrole as the key precursor. In our strategy, the pyrrole–pyrrole bond was generated to form 27-thiasapphyrins by oxidative coupling of meso-aryl dipyrromethane and 2,5-bis(p-tolylhydroxymethyl)thiophene, and the desired 27-thiasapphyrins were isolated in 8–12 % yields. The crystal structure of one of the 27-thiasapphyrins indicates that the macrocycle is almost planar and the thiophene sulfur atom is in the plane whereas the four pyrrole nitrogen atoms slightly deviate from the plane defined by four meso carbon atoms. Absorption spectroscopy showed four well defined Q bands in 590–770 nm and one strong Soret band in 470–480 nm region for 27-thiasapphyrins. The 27-thiasapphyrins are stable under redox conditions and undergo two-to-three reversible oxidations and one-to-two reversible reductions. The macrocycles are weakly fluorescent with low quantum yields and singlet state lifetimes.

Unsymmetrical 22-oxacorrole containing two aryl groups and one pyrrole group at the meso position was synthesized by condensing one equivalent of 16-oxatripyrrane with one equivalent of meso aryl dipyromethane under mild acid-catalyzed conditions followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). This [3+2] condensation approach was expected to yield meso-free 25-oxasmaragdyrin but unexpectedly afforded unsymmetrical meso-pyrrole-substituted 22-oxacorrole. We demonstrated the versatility of the reaction by synthesizing four new meso-pyrrole-substituted 22-oxacorroles. The reactivity of α-position of meso-pyrrole was tested by carrying out various functionalization reactions such as bromination, formylation, and nitration and obtained the functionalized meso-pyrrole-substituted 22-oxacorroles in decent yields. The X-ray structure obtained for one of the functionalized meso-pyrrole substituted 22-oxacorrole revealed that the macrocycle was nearly planar and the meso-pyrrole was in the perpendicular orientation with respect to the macrocyclic plane. The meso-pyrrole-substituted 22-oxacorroles absorb strongly in 400–700 nm region with one strong Soret band and four weak Q bands. The 22-oxacorroles are strongly fluorescent and showed emission maxima at ≈650 nm with decent quantum yields and singlet-state lifetimes. The 22-oxacorroles are redox-active and exhibited three irreversible oxidations and one or two reversible reduction(s). A preliminary biological study indicated that meso-pyrrole corroles are biocompatible.

A simple, one-step, supramolecular strategy was adopted to synthesize Sn^IV-porphyrin-based axially bonded triads and higher oligomers by using meso-pyridyl Sn^IV porphyrin, meso-hydroxyphenyl-21,23-dithiaporphyrin, and Ru^II porphyrin as building blocks and employing complementary and non-interfering Sn^IVO and Ru^II⋅⋅⋅N interactions. The multiporphyrin arrays are stable and robust and were purified by column chromatography. ¹H, ¹H–¹H COSY and NOESY NMR spectroscopic studies were used to unequivocally deduce the molecular structures of Sn^IV-porphyrin-based triads and higher oligomers. Absorption and electrochemical studies indicated weak interaction among the different porphyrin units in triads and higher oligomers, in support of the supramolecular nature of the arrays. Steady-state fluorescence studies on triads indicated the possibility of energy transfer in the singlet state from the basal Sn^IV porphyrin to the axial 21,23-dithiaporphyrin. However, the higher oligomers were weakly fluorescent due to the presence of heavy Ru^II porphyrin unit(s), which quench the fluorescence of the Sn^IV porphyrin and 21,23-dithiaporphyrin units.

Treatment of six-coordinate (5,10,15-triphenylcorrole)dihydroxyphosphorus(V) [P(TPC)(OH)₂] with trifluoroacetic acid (TFA) in CH₂Cl₂ for 30 min at room temperature followed by recrystallization gave stable five-coordinate (5,10,15-triphenylcorrole)oxophosphorus(V) [P(TPC)O] in quantitative yield. The formation of [P(TPC)O] from [P(TPC)(OH)₂] in the presence of TFA was also monitored by NMR, absorption and fluorescence spectroscopic titration studies. The structure of the isolated [P(TPC)O] was confirmed by X-ray crystallography. In [P(TPC)O], the corrole ring is distorted, and the P^V ion is displaced by 0.456 Å from the N₄ plane towards the axial oxygen atom. This is unlike six-coordinate (5,10,15-triphenylcorrole)dimethoxyphosphorus(V) [P(TPC)(OCH₃)₂], in which the P^V ion lies in the porphyrin plane. NMR, absorption and fluorescence spectroscopy and electrochemical studies indicate that [P(TPC)O] exhibits interesting and distinct properties, which differ from the six-coordinate [P(TPC)(OCH₃)₂]. Attempts to reduce the P^V complex [P(TPC)O] to its corresponding P^III complex by treating it with LiAlH₄ resulted in the formation of six-coordinate (5,10,15-triphenylcorrole)dihydridophosphorus(V) [P(TPC)H₂].

The synthesis, spectroscopic, and electrochemical properties of seven new P^V–meso-triarylcorroles (1–7) are reported. Compounds 1–7 were prepared by heating the corresponding free-base corroles with POCl₃ at reflux in pyridine. Hexacoordinate P^V complexes of meso-triarylcorroles were isolated that contained two axial hydroxy groups, unlike the P^V complex of 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole, which was pentacoordinate, or the P^V complex of meso-tetraphenylporphyrin, which was hexacoordinate with two axial chloro groups. ¹H and ³¹P NMR spectroscopy in CDCl₃ indicated that the hexacoordinated P^V–meso-triarylcorroles were prone to axial-ligand dissociation to form pentacoordinated P^V–meso-triarylcorroles. However, in the presence of strongly coordinating solvents, such as CH₃OH, THF, and DMSO, the P^V–meso-triarylcorroles preferred to exist in a hexacoordinated geometry in which the corresponding solvent molecules acted as axial ligands. X-ray diffraction of two complexes confirmed the hexacoordination environment for P^V–meso-triarylcorroles. Their absorption spectra in two coordinating solvents revealed that P^V–meso-triarylcorroles showed a strong band at about 600 nm together with other bands, in contrast to P^V–porphyrins, which showed weak bands in the visible region. These compounds were easier to oxidize and more difficult to reduce compared to P^V–porphyrins. These compounds were brightly fluorescent, unlike the weakly fluorescent P^V–porphyrins, and the quantum yields for selected P^V–corroles were as high as Al^III and Ga^III corroles, which are the best known fluorescent compounds among oligopyrrolic macrocycles.

The stable and robust cyclotriphosphazene and cyclotetraphosphazene rings were used as scaffolds to prepare hexa- and octaporphyrin arrays by treating N₃P₃Cl₆ and N₄P₄Cl₈, respectively, with 5-(4-hydroxyphenyl)-10,15,20-tri(p-tolyl)porphyrin (N₄ core) or with its thiaporphyrin analogues (N₃S and N₂S₂ cores) in THF in the presence of Cs₂CO₃ under simple reaction conditions. Thiaporphyrins were examined in addition to the normal porphyrin to tune the electronic properties of the resultant arrays. Observation of the molecular ion peaks in the mass spectra confirmed the molecular structures of the arrays. 1D and 2D NMR techniques were employed to characterize the multiporphyrin arrays in detail. The ¹H NMR spectra of the multiporphyrin arrays each show a systematic set of signals, indicating that the porphyrin units are arranged in a symmetrical fashion around the cyclophosphazene rings. All signals in the ¹H NMR spectra were assigned with the aid of COSY and NOESY experiments. The protons of each porphyrin unit are subject to upfield and downfield shifts because of the ring-current effects of neighboring porphyrin units. Optical, electrochemical, and fluorescence studies of the arrays indicated that the porphyrin units retain their independent ground- and excited-state characteristics. Cu^II and Ni^II derivatives of hexaporphyrin and octaporphyrin arrays containing N₄ porphyrin units and N₃S porphyrin units were synthesized, and complete metalation of the arrays was confirmed by their mass spectra and by detailed NMR characterization of the Ni^II derivatives of hexa- and octaporphyrin arrays containing N₄ porphyrin units. Electrochemical studies indicated that Cu^II and Ni^II ions present in the thiaporphyrin units of the arrays can be stabilized in the +1 oxidation state, which is not possible with arrays containing normal porphyrin units.

Mono-functionalized core-modified sapphyrin (with a N₂S₃ core) and smaragdyrin (with a N₄O core) containing a meso-iodophenyl functional group were synthesized by following a [3+2] condensation approach using appropriate precursors. The mono-functionalized sapphyrin and smaragdyrin building blocks were used to synthesize the first examples of diphenyl ethyne bridged porphyrin–sapphyrin and porphyrin/Zn^IIporphyrin–smaragdyrin dyads under mild Pd⁰-coupling conditions. The dyads are freely soluble in common organic solvents and were characterized by various spectroscopic techniques. Photophysical studies indicated the possibility of energy transfer from the porphyrin/Zn^II porphyrin sub-unit to the smaragdyrin sub-unit in porphyrin/Zn^IIporphyrin–smaragdyrin dyads. The potential of these dyads as fluorescent sensors for anions was explored. The studies indicated that the porphyrin–sapphyrin dyad cannot be used as fluorescent sensors, whereas the porphyrin–smaragdyrin dyad was suitable.

A series of mono-functionalized core-modified expanded porphyrin building blocks such as thiasapphyrin, thiarubyrin, oxasmaragdyrin, and BF₂–oxasmaragdyrin have been synthesized by simple condensation of readily available precursors. The mono-functionalized core-modified expanded porphyrin building blocks were used to synthesize the first three examples of covalently linked diphenylethyne-bridged dyads containing two different expanded porphyrin macrocycles, namely thaisapphyrin–BF₂–oxasmaragdyrin, thiarubyrin–BF₂–oxasmaragdyrin, and thiasapphyrin–thiarubyrin, by coupling appropriate mono-functionalized expanded porphyrin building blocks under mild Pd⁰ coupling reaction conditions. The three dyads were freely soluble in common organic solvents and characterized by MS, NMR, absorption, electrochemical, and fluorescence techniques. The NMR, absorption, and electrochemical studies indicated that the two macrocycles in the dyads interact weakly with each other and maintain their independent characteristic features. The steady-state fluorescence studies of the dyads showed that the thiasapphyrin and thiarubyrin units are nonfluorescent but fluorescence was observed from the BF₂–oxasmaragdyrin unit. However, the quantum yield of the BF₂–oxasmaragdyrin unit in the dyads was less than that of monomeric BF₂–oxasmaragdyrin because of an enhancement of nonradiative decay channels operating in the dyads. The potential use of two of the three dyads containing the BF₂–smaragdyrin subunit as fluorescent sensors for anions was explored. The studies showed that the binding of the anion at the protonated sapphyrin and rubyrin sites in the respective dyads can be followed by the clear changes in the fluorescence band of the BF₂–oxasmaragdyrin unit, which indicates that these dyads can be used as fluorescent anion sensors.

Four covalently linked trichromophore systems containing a central boron dipyrromethene (BODIPY) unit connected to a porphyrin unit through the 3-position and a core-modified porphyrin or a porphyrin expanded through the 5-position were synthesized by treating 3-bromo-5-porphyrinyl BODIPY or 3-bromo-5-rubyrinyl BODIPY with the corresponding hydroxy porphyrin or hydroxy-expanded porphyrin in CHCl₃ at 60 °C. The compounds are freely soluble in common organic solvents and confirmed by mass spectrometry and 1D and 2D NMR spectroscopy techniques. The absorption and electrochemical studies support weak ground-state interactions among the three chromophore units within the trichromophore systems. The fluorescence studies indicate that BODIPY emission is quenched to a significant degree in all trichromophore systems due to a transfer of energy to one or both macrocyclic units attached to the BODIPY chromophore.

A simple method has been used to synthesize four porphyrin azides with cores such as N₄, N₃S, N₂SO and N₂S₂ in 60–90 % yields by treating the corresponding aminoporphyrins with tert-butyl nitrite (tBuONO) and azidotrimethylsilane (TMSN₃) in THF/CH₃CN under mild reaction conditions. The hitherto unknown aminoporphyrins with heteroatom cores were synthesized from their corresponding nitroporphyrins by standard SnCl₂/HCl reduction. The azidoporphyrins were used to synthesize six triazole-bridged unsymmetrical porphyrin dyads containing two different types of porphyrin sub-units as well as five triazole-bridged porphyrin–ferrocene conjugates under Cu^I-catalyzed “click” reaction conditions. Various Cu^I-catalyzed reaction conditions were studied and the best yields of triazole-bridged dyads and conjugates were obtained with CuI/DIPEA in THF/CH₃CN at room temperature for overnight. The unsymmetrical porphyrin dyads and porphyrin–ferrocene conjugates were characterized by various spectroscopic and electrochemical techniques. In unsymmetrical porphyrin dyads, the NMR, absorption and electrochemical studies indicate a weak interaction between the two porphyrin sub-units. However, preliminary photophysical studies support an efficient singlet-singlet energy transfer from one porphyrin unit to another in five unsymmetrical dyads reported here. In porphyrin–ferrocene conjugates, the fluorescence of porphyrin was quenched significantly due to photo-induced electron transfer from ferrocene to porphyrin.

The first examples of β,meso-acetylenyl-bridged, asymmetrical, covalently linked, porphyrin dyads, containing two different subunits, such as ZnN₄P-N₃OP (1), ZnN₄P-N₃SP (2), ZnN₄P-N₂SOP (4) and ZnN₄P-N₂S₂P (6), were synthesized by the coupling of a β-acetylenyl, ZnN₄ porphyrin with a meso-bromoheteroporphyrin under mild, Pd⁰-catalyzed, coupling conditions. The dyads containing different types of metal-free subunits, such as N₄P-N₃SP (3), N₄P-N₂SOP (5) and N₄P-N₂S₂P (7), were synthesized by the demetallation of the corresponding dyads. The seven β,meso-acetylenyl dyads 1–7 were characterized by NMR, MS, absorption, fluorescence and electrochemical techniques. The NMR, absorption and electrochemical studies support an electronic interaction between the subunits in all seven dyads. The steady-statefluorescence studies on dyads 1–7 support an efficient energy transfer from the donor (ZnN₄ or N₄) subunit to the acceptor heteroporphyrin subunit upon excitation of the ZnN₄/N₄ subunit. First-principle-based, quantum-chemical studies carried out on dyads 1, 2, 4 and 6 further support an electronic interaction between the donor and acceptor subunits. The computational studies also predict significant tuning of the electronic energy levels in these dyads with the modification of the porphyrin core of the acceptor groups. The calculations support the experimental results of efficient donoracceptor energy transfer in these dyads.

Nucleophilic substitution reactions of 2-, 3- and 4-hydroxypyridines with 3,5-dibromo meso-aryl and meso-furyl boron-dipyrromethenes (BODIPYs) resulted in the formation of the corresponding 3,5-bis(oxopyridinyl)-BODIPYs and 3,5-bis(pyridinyloxy)-BODIPYs in decent yields. The effect of a pyridone versus an oxypyridine at the 3- and 5-positions on the spectral, electrochemical and photophysical properties were studied as a function of solvent. The 3,5-bis(oxopyridinyl)-BODIPYs exhibit broad, red-shifted absorption and emission bands, decreased quantum yields and lifetimes, displayed large Stokes shifts and easier reductions than did the 3,5-bis(pyridinyloxy)-BODIPYs. The differences in the properties of these two classes of BODIPY dyes are attributed to the extension of π-delocalization associated with the electron-deficient nature of the pyridone groups.

A series of thiaphlorins with N₂S₂ and N₃S cores have been prepared in decent yields from readily available precursors. The thiaphlorins were characterized by all spectroscopic techniques and the structures of two thiaphlorins were solved by X-ray crystallography. The spectral studies indicated that the properties of thiaphlorins were quite different from those of thiaporphyrins. The methodology used for the synthesis of thiaphlorins has been extended to synthesize a series of monofunctionalized thiaphlorins. We also performed functional group transformation of thiaphlorins without decomposition, supporting the conjecture of the stable natures of thiaphlorins. The crystal structure analysis of two thiaphlorins indicated that the macrocycles are not planar and that they each show a marked kink at sp³-hybridised meso carbon. The functionalized thiaphlorins have been used to synthesize several novel porphyrin–thiaphlorin dyads as well as a bis(thiaphlorin) dyad under mild palladium(0) coupling conditions. Preliminary anion-binding studies carried out on thiaphlorins and porphyrin–thiaphlorin dyads indicated that they can bind anions effectively in their protonated forms and that these systems can also be used as optical sensors.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)