No abstract

A state of (con)fusion: The introduction of a confused pyrrole ring into a meso‐aryl sapphyrin framework destabilizes the macrocycle and forces a fusion reaction to occur. Subsequent metalation with rhenium results in further mutation to form a domino‐fused sapphyrin with a fused penta‐ring system (see scheme).

A rapid synthetic route has been developed to synthesize mono- and trifunctionalized 21-thia and 21-oxaporphyrin systems using simple precursors such as 2[alpha-(aryl)-alpha-hydroxymethyl] thiophene (thiophene mono-ol) and 2[alpha-(aryl)-alpha-hydroxymethyl] furan (furan mono-ol), respectively. Condensation of one equivalent of thiophene or furan mono-ol with two equivalents of aryl aldehyde and three equivalents of pyrrole under porphyrin forming conditions followed by column chromatography resulted in functionalized 21-thia or 21-oxaporphyrins. To synthesize monofunctionalized porphyrins, the mono-ol containing the functionalized aryl group was used. The functionalized aldehydes were used to synthesize trifunctionalized porphyrins. The mono-ol method is versatile and applicable to synthesize mono- and trifunctionalized 21-thia and 21-oxaporphyrins containing functional groups such as iodophenyl, ethynylphenyl, hydroxyphenyl, bromophenyl, and pyridyl groups. The monofunctionalized porphyrin building blocks containing iodophenyl and ethynylphenyl groups were used further to synthesize four unsymmetrical covalent porphyrin dimers containing two different porphyrin cores such as N3S-N4, N3O-N4, and N3S-N3O bridged via diaryl ethyne group and one symmetrical phenylethyne bridged dimer containing two N3S cores. A preliminary photophysical study on these dimers indicated a possibility of energy transfer from one subunit to another. We also demonstrated the use of trifunctionalized porphyrins in the synthesis of two noncovalent unsymmetrical porphyrin tetramers containing one N3S and three N4 porphyrin subunits.

A series of meso-thienyl-substituted porphyrins with different porphyrin cores such as N 3 S, N 2 S 2 and N 3 O were synthesized and characterized. The thienyl groups at the meso-carbon atoms change the electronic properties of the porphyrin ring. The X-ray structure solved for the N 2 S 2 porphyrin with four meso-thienyl groups showed supramolecular assembly formation in the solid state due to C−H···N hydrogen bonding Core-modified porphyrins resulting from the replacement of one or two pyrrole rings by heterocycles such as thiophene, furan, selenophene and tellurophene have received only little attention in spite of their novel properties such as stabilization of metal atoms in unusual oxidation states.[1]For example, it has been shown that 5,10,15,20-tetraphenyl-21-thiaporphyrin (N 3 S core) can stabilize copper() [2] which is not possible with a normal 5,10,15,20-tetraphenylporphyrin (N 4 core). Most of the studies on core-modified porphyrins have been directed towards the synthesis and stabilization of metal atoms of copper, nickel and rhodium in unusual oxidation states. [2] There are no studies on the effects of introducing different kinds of substituents at meso-as well as β-positions on the electronic properties of the coremodified porphyrins. Recently, there have been reports on meso-tetrathienylporphyrins with N 4 porphyrin cores.[3] The meso-tetrathienylporphyrins showed very interesting filmforming and conductivity behaviour [4] and they were also good models for energy-transfer reactions.[3a] It was also shown that by introducing the five-membered thienyl groups in place of six-membered aryl groups at meso-carbon atoms, the electronic properties were altered dramatically.[3d] The interesting electronic properties of the mesothienylporphyrins suggests that these porphyrins can be used as a substitute for meso-tetraarylporphyrins for various applications. Interestingly, there are no reports on coremodified porphyrins with five-membered heterocycles such as thienyl and furyl [5] at meso-carbon atoms to study their effect on the electronic properties of the porphyrins. In this [a] between the CH group of the meso-thienyl group of one porphyrin ring with the pyrrole N atom of another porphyrin ring. The X-ray analysis of the N 3 S porphyrin with two mesothienyl groups and two meso-aryl groups did not show any supramolecular assembly formation in the solid state.

A series of rhenium(i) dipyrrinato complexes (Re1–Re8) have been prepared and characterized; their crystal structures, phosphorescence and singlet oxygen generation studies are reported.

A novel [36]octaphyrin analogue embedding two N-confused pyrrole units demonstrated unique prototropy-coupled isomerization between the Figure-of-eight and dumbbell conformers. Upon bis-metal coordination, fixation of fully π-conjugated Figure-of-eight structures was achieved as referred from the X-ray crystal structure. Chirogenesis of the helical enantiomers was proved by intense circular dichroism (CD) response in the near infrared (NIR) region.

meso-Substituted BODIPY with N-butylcarbazole () was prepared and derivatized. Dibromo BODIPY , α-formyl BODIPY and β-formyl BODIPY were synthesized. All compounds were characterized by HRMS, NMR, UV-vis absorption, electrochemical and fluorescence techniques. The crystal structures of BODIPY and its dibromo derivative were also solved. In both the X-ray structures, the dihedral angle between the meso-carbazole group and the dipyrrin plane was decreased, suggesting the increased interaction between the two units. meso-Substitution with the N-butylcarbazole group on the BODIPY core rendered huge Stokes shifts (111-168 nm) and higher quantum yields as compared to meso-aryl BODIPY. An efficient energy transfer from the carbazole unit to the BODIPY core was observed by fluorescence spectroscopy for all the compounds . CV studies of compounds showed anodic shifts of the reduction and oxidation potentials, suggesting that the meso-carbazole group is affecting the electronic properties of the BODIPY core and making them easier to reduce.

Six donor-acceptor-type near-infrared (NIR) aza-boron-dipyrromethene (BODIPY) dyes and their corresponding aza-dipyrrins were designed and synthesized. The donor moieties at the 1,7-positions of the aza-BODIPY core were varied from naphthyl to N-phenylcarbazole to N-butylcarbazole. The 3,5-positions were also substituted with phenyl or thienyl groups in the aza-BODIPYs. Photophysical, electrochemical, and computational studies were carried out. The absorption and emission spectra of aza-BODIPYs were significantly redshifted (≈100 nm) relative to the parent tetraphenylaza-BODIPY. Fluorescence studies suggested effective energy transfer (up to 93 %) from donor groups to the aza-BODIPY core in all of the compounds under study. Time-dependent (TD)-DFT studies indicated effective electronic interactions between energy donor groups and aza-dipyrrin unit in all the aza-BODIPYs studied. The HOMO-LUMO gap (ΔE) calculated from cyclic voltammetry data was found to be lower for six aza-BODIPYs relative to their corresponding aza-dipyrrins.