Derivation-density-engineered molecular packing, emission property, mechanofluorochromism and mechanoluminescence of triarylimidazole-substitued triphenylamines

Abstract

Three fluorophores IMTPA-1, IMTPA-2 and IMTPA-3 where one, two and three 2, 4, 5-triarylimidazole (IM) moieties are grown up on a triphenylamine (TPA) core are prepared while their solution- and solid-state photophysical properties are investigated. It is found that the derivation density makes very profound impact on solvatochromic behaviors, emission wavelength and intension together with mechanofluorochromic (MFC) and mechanoluminescent activities of these compounds. As the derivation density is increased, solvatochromic effect becomes weaker. Moreover, fluorescence quenching only occurs on IMTPA-3 crystal in comparison of high emission intensity on IMTPA-1 and IMTPA-2 crystals. The three fluorophores are all MFC-active but the emission wavelengths of the amorphous samples are insensitive to the derivation density. However, mechanoluminescence (ML) effect on these crystals are highly derivation-density-dependent, as force strength needed for ML phenomena to occur is in IMTPA-1 ≫ IMTPA-2 ~ IMTPA-3 order while the ML intensity is in the contrary one. In aid of X-ray crystallography and theory calculations, a deep insight of structure-property relationship on this series in view of derivation density is obtained, which is a novel method to present compounds with differentiated MFC and/or ML activity.