Unusual fluorescene emission from ethynyltriphenylene-substituted diacetylenic molecular hinge. Formation of intramolecular excimer

Abstract

A diacetylenic molecular hinge bearing two ethynyltriphenylene units (1) has been synthesized. Evidence from ¹H NMR and variable temperature NMR (VT-NMR) of 1 in comparison to model compounds bearing only one triphenylene unit suggests that there is an equilibrium between the open conformer and the intramolecularly π–π interacting closed conformer in solution (equilibrium constant K = 6.5 at 298 K in CDCl₃) arising from the rotation of the diacetylenic hinge. Unusual fluorescence emission observed from 1 has been assigned to excimer formation arising from intramolecularly π–π interacting triphenylene units in the excited state. Steady state and picosecond time resolved fluorescence spectra of 1 were nearly identical and corresponded to intramolecular excimer emission.