Design, synthesis and properties of near-infrared molecular switches containing a fluorene ring

Abstract

Three molecular switches containing a fluorene ring were designed and synthesized. The introduction of the amino group substituted fluorene ring resulted in the target molecular switches having some optical properties in the near-infrared region. It was demonstrated that the N-substituents on the fluorene rings and the switch units both had great influence on the molecular switch optical properties including the absorption maximum, absorption intensity and fluorescence quantum yield. The open-ring forms IA and IIA showed obvious solvatochromic behaviour. The closed-ring forms IIB and IIIB showed obvious hydrochromic behaviour in MeCN/water binary solvent systems and acidichromic behaviour in MeCN solution with high reversibility. Especially, the distinct off–on fluorescence signal in the near-infrared region using the stimuli of acid means that the designed compounds have great potential application value in the field of biological sensing.