Dicyanoisophorone-Based Chromophores with Tunable Optical Responses: Synthesis, Characterization and Applications

Two dicyanoisophorone-based conjugated compounds, Compound 1 and Compound 2, were synthesized through piperidine-catalyzed Knoevenagel condensation of dicyanoisophorone with 2-hydroxy-1-naphthaldehyde and 4-methoxybenzaldehyde, respectively. The synthesized compounds were characterized using FT-IR, 1H NMR, 13C NMR, HR-MS and HPLC techniques. Compound 1 was obtained as a red solid in 84% yield with a melting point of 239 °C, while Compound 2 was obtained as a brown solid with a melting point of 88 °C. The compounds exhibited interesting optical properties. Compound 1 showed a distinct acid–base-responsive colour change, displaying yellow, orange and blue colors under neutral, acidic and basic conditions, respectively. Compound 2 exhibited enhanced fluorescence upon aggregation, indicating aggregation-induced emission behavior. Both compounds also showed fluorescence under UV irradiation, with Compound 1 exhibiting bright red fluorescence. These results demonstrate that aromatic structural modification of the dicyanoisophorone framework can effectively tune its optical properties, highlighting the potential of these compounds for colourimetric sensing and fluorescence-based applications.