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

Abstract

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.