Design, synthesis and photoswitching of broad-spectrum fluorescent hexaarylbiimidazoles

Abstract

A series of novel hexaarylbiimidazole (HABI)-containing fluorophores with broad-spectrum emissions ranging from blue, green and red emissions, have been designed and synthesized. Their photochromism and fluorescence switching properties are investigated by UV-Vis absorption and fluorescence spectra in solutions and PMMA films. By connecting carbazole (Cz), naphthalimide (NI) and perylene-mono-imide (PMI) to HABI with a spacer, three molecular photoswitches with broad-spectrum fluorescence varying from deep blue (Cz–O–HABI, λ_em = 390 nm, Φ_F = 0.27), green (NI–O–HABI, λ_em = 490 nm, Φ_F = 0.25) to far red (PMI–O–HABI, λ_em = 650 nm, Φ_F = 0.25) have been obtained. The “ON”/“OFF” ratios are calculated to be about 8.9, 8.0 and 3.7 (calculated from FL spectra) for Cz–O–HABI, NI–O–HABI and PMI–O–HABI, respectively. Such a series of photoswitchable fluorophores constitute prototypes of a photochromic molecular library in which fluorescence resonance energy transfer can be reversibly modulated by an external stimulus, namely, UV light.