Rationally Designed Maleimide Dyes for Large Stokes Shifted Solvatochromism and Aggregation-Induced Emission

Tuning of photophysical characteristics of small molecule fluorophores by simple synthetic method is desired but possesses its own challenges. We are reporting here an easy-to-achieve synthetic strategy to tune N-H maleimide-based fluorescent small molecules 2a-c to achieve large Stokes shifted solvatochromism and aggregation induced emission (AIE) via. π-surface extension. Fluorophore 2a-c exhibit broad solvatochromic emission range from blue to yellow (458 to 568 nm) due to intramolecular charge transfer with incremental large Stokes shift (110 nm to 192 nm) in nonpolar to polar solvent. The introduction of the phenyl ring affects both the electronic conjugation and the facile aggregation in the bad solvent. Along with synthesis, thermal stability and detailed photophysical study of the synthesized fluorophores and study of AIE in the THF/water mixture of a representative probe (2c) is presented. Moreover, the experimental results are well supported by the DFT study.