Dual-state emission of D-A-D type benzothiadiazole derivatives for the sensitive detection of amine compounds

Organic light-emitting materials with dual-state emission (DSE) in both solution and solid states have attracted widely attention because of their promising applications in diverse areas. In this work, five benzothiadiazole-based D-A-D type luminogens BT2Ph, BT2Na, BT2Pa, BT2An and BT2Py were concisely synthesized by introducing different π–conjugated rigid groups (benzene, naphthalene, phenanthrene, anthracene and pyrene ring). As a result of their twisted conformation and effective conjugation structure, these five dual-state emission molecules exhibit intense photoluminescence in solution and solid state. The reason for these luminogens with DSE behavior was further explained by the twisted intramolecular charge-transfer mechanism based on the variable temperature fluorescence spectrum measurement and theoretical calculation with time-dependent density functional theory (TD-DFT). Moreover, these DSE luminogens which possess excellent photostability and obvious solvatofluorochromic properties were multifunctional fluorescent probes for the visual detection of amine compounds (aniline, cyclohexylamine, and ammonia). A charge transfer mechanism between luminogens and amine compounds was found to be the cause of fluorescence quenching. Thus, these DSE molecules may have applications in anti-counterfeiting and fluorescent sensors.