Acenaphthenone derived thermally stable, solid state emissive, AIEgenic, and viscosity sensitive methine dyes with enhanced linear properties: Synthesis and DFT studies

Abstract

Acenaphthenone-derived methine derivatives are synthesized by oxidation of acenaphthene to acenaphthenone (I) followed by Knoevenagel condensation using malononitrile, benzothiazole acetonitrile, benzimidazole acetonitrile. The resulting molecules - I-1, I-2, and I-3 show absorption ⁓ 300–600 nm and emission ⁓ 360–500 nm range, respectively, in THF, MeOH, DMF, and DMSO. I-1, I-2, and I-3 also displayed solid-state emission at 515 nm, 517 nm, and 574 nm, respectively. Further, these derivatives were found sensitive toward viscous, acidic, and basic environments. I-1 and I-2 displayed aggregation-induced emission in THF:distilled water system. They show thermal stability ⁓ 250 °C. DFT studies revealed that these molecules are an electron-rich system with a planar geometry. The electron density is evenly distributed throughout the skeleton in both HOMO and LUMO. TD-B3LYP/6–311++G(d,p), TD-CAM-B3LYP/6–311++G(d,p), and experimental absorption maxima showed the same trend in THF. Vertical excitation is mainly assigned to HOMO → LUMO transition with % orbital contribution ⁓ 94–98 % and oscillator strength in the 0.09–0.93 range. These molecules can show linear properties exclusively.