Synthesis, structural, and photophysical studies of π-fused acenaphtho[1,2-d]imidazole-based excited-state intramolecular proton transfer molecules

Orange-red fluorescent molecules are promising materials for use in a new generation of displays, light sources, and chemosensors because conventional red-emitters have lower fluorescence quantum efficiencies. In this work, a set of orange-emitting fused imidazole series 2-(7-(4-fluoropheny1)-7H-acenaphtho[1,2-d]imidazol-8-yl)phenol(AHPI-F), 2-(7-(4-chlorophenyl)-7H-acenaphtho[1,2-d]imidazol-8yl)phenol (AHPI-C1), and 2-(7-(4-bromophenyl)-7H-acenaphtho[1,2-d]imidazol-8-yl)phenol (AHPI-Br) have been synthesized via multicomponent reaction method with high yield. Synthesized molecules were fully characterized by H-1 NMR, C-13 NMR, GC-Mass, UV vis. absorption, PL, and TGA-DSC. The compounds AHPI-F, AHPI-C1, AHPI-Br showed large Stokes' shifted emission due to excited -state intramolecular proton transfer (ESIPT) process, and they effectively formed large single crystals. The crystal structure of each compound was identified by X-ray crystallographic analysis. To elucidate the photo physical properties of the molecule, theoretical calculation were performed by density functional theory (DFT) with B3LYP 6-31G(d,p) basis sets using the identified molecular conformations from X-ray analysis. Calculated electronic properties including HOMO-LUMO levels were compared with the experimental results. As a result of ESIPT process, extended conjugation length through acenaphto[1,2-d]imidazole, and charge transfer characteristics by the introduction of halogen atoms, all of the materials showed orange ESIPT emission with no spatial overlap between absorption (lambda(max,abs) = 325 nm) and emission (lambda(max,ems) = 578 nm). (C) 2017 Elsevier B.V. All rights reserved.