Alkoxy chain engineering in diphenylamine-based fluorophores: Achieving red-shifted near-infrared aggregation-induced...

The evolution of organic fluorophores with adequate solid-state or aggregated-state emissions in near-infrared (NIR) region is still demanding. In this study, we synthesize a series of NIR fluorophores (1DL, 3DL and 5DL) with aggregation-induced emission (AIE) characteristics by modifying alkoxy chains in diphenylamine, using 0DL as the structural template. Through the modification of alkoxy chains in these compounds, these fluorophores exhibit longer absorption and emission wavelengths with large Stokes shift up to 204 nm. Compared with 0DL, the absorption and emission peaks of 1DL, 3DL and 5DL are red-shifted by approximately 70 nm. Furthermore, 1DL, 3DL and 5DL possess the narrowing HOMO-LUMO energy gaps comparing to 0DL, which are coincident with the red-shift of absorption and emission spectra owing to the enhancement of D-A interaction. Among them, the absorption and emission peaks of 3DL are 683 nm and 887 nm, respectively. The bioimaging performance of the 3DL encapsulated within Pluronic F127 demonstrates potentiality as NIR fluorescent probe for biological applications. Therefore, this work presents a valued strategy for the evolution of efficient NIR fluorescent probe.