Yuan Dai

Simultaneous enhancement of fluorescence and solubility by N-alkylation and functionalization of 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline with heterocyclic bridges

A family of 2-(2-thienyl)imidazo[4,5-f][1,10]-phenanthroline (TIP) based compounds with large delocalized π systems has been designed and synthesized following the strategy of introducing alkyl chains and extending different S-, N- and O-containing aromatic heterocyclic tails. Simultaneous enhancements of the fluorescence emission and solubility in organic solvents for the resultant aromatic heterocyclic compounds 1–13 have been achieved. Analyses on twelve X-ray single-crystal structures indicate that the thiophene ring of the TIP unit in this series of compounds shows the same trans configuration with its imidazo[4,5-f][1,10]-phenanthroline core but different dihedral angles with the adjacent aromatic heterocycles. Thermal gravimetric analyses for ten imidazole N-substituted TIP derivatives reveal that they still retain good thermal stability with decomposition temperatures higher than 300 °C originating from their common TIP core, even with the introduction of the n-butyl radical in their molecular structure. Moreover, TPA and carbazole substituted compounds 2 and 9 were used as the ancillary ligands to prepare their corresponding ruthenium(II) sensitizers, BM3 and BM4, and their dye-sensitized solar cell performance was evaluated.

N-Acylamino-pyridine-2,6-dione based heterocyclic dyes and their oxidative ring-degradation under alkaline conditions

Three new N-acylamino-pyridine-2,6-dione compounds have been synthesized, which are used for the first time as coupling components to prepare corresponding heterocyclic dyes. These dyes exhibit the same hydrazone-tautomeric form both in the solid state and in solution, which have been verified by X-ray single-crystal structures and 1H NMR spectra, respectively. The reversible acid–base discoloration of the dyes has been studied via pH titration experiments, which is ascribed to the interconversion between the hydrazone and deprotonated azo forms, as evidenced by the isoabsorptive point in their UV-Vis spectra. Comparisons of their dyeing performance have been made with five commercially available pyridine-2,6-dione based disperse yellow dyes. In terms of the current problems of alkaline and oxygen instability for pyridine-2,6-dione based disperse dyes in the dyeing process, the oxidation of these dyes under alkaline conditions is further explored and three ring-degradation (ring-opening and subsequent oxidative cleavage) products are yielded. Our results clearly demonstrate that the relatively poor basic stability of pyridine-2,6-dione based dyes under oxidative conditions originates from the ring-opening of the amide unit and subsequent oxidative cleavage of the CC double bond in the pyridine-2,6-dione ring.