Synthesis, photophysical behavior in solution, aggregates, solid state and computational study of new derivatives of 2,2′-bis(indolyl)methane-triphenylamine

Abstract

A series of new 2,2′-bis(indolyl)methane-triphenylamine (2,2′-BIM-TPA) derivatives were synthesized and characterized. TPA units were inserted in the indole fragment, as well as in the methylene position of the BIM to obtain systems with a high degree of torsion and intramolecular rotation. Phenyl and phenylethynyl linkers between TPA and BIM units were included in the BIM-Ph-TPA and BIM-Ph-E-TPA derivatives to extend the conjugation of the methylene substituted BIMs. The absorption and emission behavior in solution, aggregates and solid state of five 2,2′-BIM-TPA derivatives was studied. Only BIM-Ph-TPA and BIM-Ph-E-TPA showed a slight solvatochromic behavior. In THF-water mixtures, non-emissive aggregates were produced, but the concentrated solutions (1000 µM) of each compound favored the formation of emissive aggregates. It was found that water acts as a fluorescence quencher of the aggregates. Additionally, the 2,2′-BIM-TPA derivatives showed fluorescence in the solid state. The DFT computational studies allowed to confirm the highly twisted molecular geometries, to elucidate the distribution and energy of the frontier molecular orbitals (HOMO-LUMO), as well as the nature of the main electronic transitions (UV–Vis).