Imidazole-Based Excited-State Intramolecular Proton-Transfer Materials:Synthesis and Amplified Spontaneous Emission from a Large Single Crystal

摘要

We have synthesized a novel class of imidazole-based excited-state intramolecular proton-transfer (ESIPT) materials,i.e.,hydroxy-substituted tetraphenylimidazole (HPI) and its derivative HPI-Ac,which formed large single crystals exhibiting intense blue fluorescence and amplified spontaneous emission (ASE).Transparent,clear,and well-defined fluorescent single crystals of HPI-Ac as large as 20 mm x 25 mm x 5 mm were easily grown from its dilute solution.From the X-ray crystallographic analysis and semiempirical molecular orbital calculation,it was deduced that the four phenyl groups substituted into the imidazole ring of HPI and HPI-Ac allowed the crystals free from concentration quenching of fluorescence by limiting the excessive tight-stacking responsible for intermolecular vibrational coupling and relevant nonradiative relaxation.Fluorescence spectral narrowing and efficient ASE were observed in the HPI-Ac single crystal even at low excitation levels attributed to the intrinsic four-level ESIPT photocycle.