Photoinduced enhancement of intraligand charge-transfer of a crystalline 3,3′-diindolyl(3-pyridyl)methane

Abstract

A charge-transfer crystalline solid of 3,3′-diindolyl(3-pyridyl)methane with solvated methanol (PMDI·MeOH) was synthesized and structurally characterized. Upon UV irradiation, the colorless PMDI·MeOH crystal became more intense orange, which could be attributed to the intraligand charge-transfer through the unit cell shrinkage caused by the intermolecular contraction between PMDI and methanol molecules, and a crystalline defect, as investigated by X-ray structural analysis, nuclear magnetic resonance, mass spectroscopy, thermal analysis, and computational studies.