Design, synthesis, fluorescence properties, and multifunctional applications of large conjugated 3-cyanocoumarin derivatives.

Coumarins, as widely used organic small molecules, have been extensively exploited for the construction of fluorescent probes. However, there are relatively few reports on their multifunctional applications and the related researches on the structure-activity relationship. In this work, two 3-cyanocoumarin compounds named as MC and MBC with aggregation-induced emission (AIE) characteristics were designed and synthesized. Due to its excellent optical properties, MBC has been developed as a fluorescent anti-counterfeiting ink. In addition, MBC can also be used as a fluorescent probe for detecting some typical nitroaromatic compounds (NACs), such as picric acid (PA) and 2,4-dinitrophenol (DNP), with limits of detection as low as 3.79 × 10-8 and 6.20 × 10-8 M, respectively. At the same time, two D-π-A type near-infrared fluorescent molecules named as MC-TPA and MBC-TPA were designed and synthesized by using two 3-cyanocoumarins (MC and MBC) as electron acceptors and 4-formyl triphenylamine (TPA) as an electron donor, respectively. Both MC-TPA and MBC-TPA molecules can exhibit AIE characteristics and obvious mechanofluorochromic (MFC) behavior. Due to the excellent color contrast, MC-TPA has been employed for inkless writing. Notably, it can be reused after being erased with dichloromethane (DCM) vapor. Based on single-crystal analysis and theoretical calculations, the structure-activity relationship accounting for diverse functional performances was explored. This serial work provides a solid foundation for the design, synthesis, and application of novel multifunctional fluorescent molecules.