Synthesis and Optical and Theoretical Characterization of Imidazo[5,1-a]isoquinolines and Imidazo[1,5-a]quinolines

Abstract

Imidazo[1,5-a]quinolines emit intense blue luminescence, suggesting their possible use as emitter molecules in organic light-emitting diodes. We synthesized several new imidazo[5,1-a]isoquinolines and found they possessed a characteristic hypsochromic effect and even increased quantum efficiency compared to the homolog imidazo[1,5-a]quinolines, as measured by UV-vis- and fluorescence spectroscopy in solution. The energies of the highest occupied and lowest unoccupied molecular orbitals were calculated using density functional theory and experimentally determined by cyclic voltammetry in solution. We obtained a maximum fluorescence quantum yield of 48 % at 446 nm for the newly synthesized 3-(4-cyanophenyl)-1-(pyridyl)imidazo[5,1-a]isoquinoline with an optimized substitution pattern. For 1-phenyl-3-(2-pyridinyl)imidazo[5,1-a]isoquinoline, a quantum yield of 33 % was obtained at an even shorter emission wavelength of 431 nm.