Isomer effect study of pyridinium-type cationic fluorophores: multiple functions and internal optical mechanisms†

Cationic fluorophores (CFs) with a highly twisted conformation are essential functional materials in the field of optical sensing and imaging. In this study, isomers of pyridinium-type CFs (PyrCFs, o-, m-, and p-TPA-Pyr-BP) were employed as three models that share the same electron donor of triphenylamine (TPA) and acceptor of pyridinium (Pyr) but with different link positions. For the purpose of demonstrating the isomer effect of o-, m-, and p-TPA-Pyr-BP, extensive investigations, including those into aggregation-induced emission (AIE) capability, sensing ability and the cell-imaging behavior, were systematically performed. Furthermore, based on the experimental findings and theoretical calculations, a deeper understanding of the internal optical mechanism is revealed. Finally, p-TPA-Pyr-BP was verified as a highly powerful multifunctional material that could be successfully used in various applications.