Narrow Results

The preparation of a new zinc(II) metalloporphyrin, substituted with four alkylated carbazole moieties, by reaction of pyrrole and 3-formyl-9-hexylcarbazole is reported. The substitution pattern negatively shifts the redox potentials of the macrocycle and leads to a material that emits green light at 615 nm when photo-excited at 554 nm.

Four different types of alternating copolymers, named as poly(N-(2-ethylhexyl)-3,6-dibromo-carbazole-alt-aniline) (P1), poly(3,6-dibromo-carbazole-alt-aniline) (P2), poly(N-(3,5-dibromo-methylene-phenyl)-carbazole-alt-aniline) (P3) and poly(N-[4-(2-ethylhexyloxyl)-3,5-dibromomethylene-phenyl]-carbazole-alt-aniline) (P4) were successfully synthesized by palladium-catalyzed polycondensation of corresponding carbazole-containing dibrominated compounds and an aniline. These resulting polymers exhibited good solubility in normal organic solvents and showed relatively high molecular weights. Excellent thermal stability of the polymers was observed from TGA, showing less than 8% of weight loss on heating to 350°C under N₂ atmosphere. From UV-Vis absorption and photoluminescence spectra of these solution-processable polymers, it was observed that λ_max,UV was in the range of 308 – 352 nm and λ_max,PL was in the blue emission range of 450 – 463 nm. Electrochemical characteristics of these alternating copolymers were investigated to prove the potential in application for blue-emitting host matrix and hole-transporting layer in polymer light-emitting devices.

A new subporphyrin namely, hydroxo-5,10,15-tri($N$-propyl-3-carbazolyl)subporphyri natoboron(III) 6 has been synthesized via the reported litreture procedure by the condensation of pyridine-tri-$N$-pyrrolylborane with 9-propyl-9H-carbazole-3-carbaldehyde. Its porphyrin analog $i.e$. 5,10,15,20-tetra($N$-propyl-3-carbazolyl)porphyrin has also been isolated from the reaction mixture, formed due to scrambling process and complexed with Zn(II). Photophysical properties of both subporphyrin and Zn(II)porphyrin have been studied in detail to confirm the intramolecular charge transfer process in subporphyrin analog. In addition, the ring contracted congener 6 also displays solid state fluorescence.

Novel octa-phenotiazine, octa-benzoazepine and octa-carbazole substituted magnesium(II) (MgPz-I-III) and zinc(II) (ZnPz-I-III) porphyrazines were synthesized from 2,3-bis[6-(4a,10a-dihydro-phenothiazin-10-yl)-hexylsulfanyl]-but-2-enedinitrile (5), 2,3-bis [6-(4a,11a-dihydro-dibenzo[b,f]azepin-5-yl)-hexysulfan-yl]-but-2-enedinitrile (8) and 2,3-bis(6-carbazol-9-yl-hexylsulfanyl)-but-2-enedinitrile (10), respectively. These dinitrile derivatives 5, 8 and 10 were also prepared by the reaction of 1,2-dicyano-1,2-ethylenedithiolate di-sodium salt (4) with 10-(6-bromohexyl)-10H-phenothiazine (3), 5-(6-bromohexyl)-5H-diben-zo[b,f]azepine (7) and 9-(6-bromo-hexyl)-9H-carbazole (9), respectively. Porphyrazino-zinc(II) complexes were synthesized by one-step reaction using Zn(BuO)${}_{\mathrm{\text{2}}}$ as a template agent. All the novel compounds were characterized by elemental analysis and different spectroscopic methods such as ${}^{\mathrm{\text{1}}}$H NMR, ${}^{\mathrm{\text{13}}}$C NMR, FT-IR, UV-Vis and mass. The photochemical properties including photodegradation and singlet oxygen generation for magnesium(II) and zinc (II) porphyrazine complexes were studied in dimethylsulfoxide solutions for determination of their photosensitizer behaviors.

Porphyrins are tetrapyrrolic aromatic macrocycles and ubiquitous in nature. They are excellent dyes with strong absorption in the visible region (400–700 nm) and they exhibit decent fluorescence in the red region (620–900 nm). Carbazole is a nitrogen-containing electron rich aromatic heterocycle which can be linked to porphyrins and other chromophores. This review provides an overview of the different synthetic strategies that have been employed to prepare carbazole-substituted porphyrins and carbazole-fused porphyrinoids and similar systems. It also shows that how the substitution of carbazole occurs on the porphyrin core can alter its optical and electronic features. Introduction of carbazole moieties in the porphyrin ring resulted in fused porphyrinoids with changed aromaticity and significantly altered electronic features of the molecules.

Chiral carbazole-based porphyrins were synthesized for the first time via the incorporation of hydrobenzoin units at the thiophene moieties. They showed absorption and circular dichroism in the near-infrared (NIR) region. The NIR absorption was further red-shifted by solvent-induced aggregation.

We report two corrole based donor–acceptor (D–A) dyads, Cbz-Cor and Ptz-Cor to understand the energy/electron transfer reactions. In these D–A systems, the donor, either carbazole (Cbz) or phenothiazine (Ptz), is covalently connected at the meso-phenyl position of 10-(phenyl)-5,15-bis-(pentafluorophenyl)corrole (Ph-Cor) by C–N linkage. Both the dyads were characterized by ¹H NMR, MALDI-TOF MS, UV-vis, electrochemical, computational methods, study state fluorescence and TCSPC techniques. A comparison of absorption spectra with their reference monomeric compounds (Cbz-Ph, Ptz-Ph and Ph-Cor) revealed minimal ground-state interactions between chromophores in both dyads. Fluorescence studies suggested that singlet–singlet energy transfer from ¹Cbz* to corrole is the major photochemical pathway in the Cbz-Cor dyad with a quenching efficiency of $\sim$99%. Detailed analysis of the data suggests that Forster’s dipole–dipole mechanism does not adequately explain this energy transfer. However, at a 410 nm excitation, florescence quenching is detected in Ptz-Cor (49%) supporting a photo induced electron transfer (PET) process from the ground state of PTZ to the excited state of corrole macrocycle. The electron-transfer rates ($k_{ET})$ of Ptz-Cor are found in the range $0.6\times 10^7$ to $1.24\times 10^8{\mathrm{\text{s}}}^{-1}$ and are concluded to be solvent dependent.

Amphiphilic carbazole pyridinium conjugates are synthesized and characterized by IR, ¹H and ${}^{13}$C NMR and ESI-MS spectrometry. The pyridinium group is attached on the 3-position of the carbazole ring and long alkyl chains are linked to the central $N$ atom. The introduction of a pyridinium group afforded water-soluble carbazole derivatives with significant bathochromic shifts in their absorption and emission spectra. As compared to the parent $N$-butylcarbazole compound, carbazole pyridinium conjugates exhibited 50 nm red-shifted absorption maxima. Similarly, the carbazole pyridinium conjugates displayed 143–147 nm red-shifted emission maxima in solution. In addition, large Stokes shifts (5747–7558 cm${}^{-1})$ were observed for the conjugates in solution. The cell penetrable amphiphilic carbazole pyridinium conjugates exhibited cytoplasmic distribution in A549 cells.

As a new family of porphyrinoids with broad absorption bands that efficiently harvest sunlight, the metal complexes of a porphyrin quadruply substituted with $N$-carbazolyl groups at the meso positions were photometrically and structurally characterized. The porphyrins exhibited characteristic broad bands in the range of 450–500 nm, due to the charge transfer band from carbazole to porphyrin. Ligand exchange at the axial position of the zinc complex with an aquo ligand affected the absorption spectrum, and a hyper-hypsochromic shift of the broad band was observed by the coordination of methanol. Furthermore, the lowest unoccupied molecular orbital (LUMO) levels of the metalloporphyrins were lowered by the electron-withdrawing effect of the perpendicularly oriented carbazolyl groups. In the solid state, zinc-porphyrin was self-assembled into a one-dimensional coordination polymer by intermolecular axial coordination.