New Potential Fluorogenic Dyes with an Extended π-System Based on Arylidene-Azolones

Objective: A new library of arylidene-imidazolones and arylidene-rhodanines with an extended π-system is presented. Methods: A tandem Wittig-hydrolysis reaction was used for the synthesis of cinnamaldehydes. Arylallylidene-imidazolones were synthesized through formation of imines of the corresponding cinnamaldehydes and subsequent [3+2] cycloaddition reaction. Knoevenagel condensation of the corresponding cinnamaldehydes with rhodanine was used for the synthesis of arylallylidene-rhodanines. The optical properties of all the new compounds were studied. Results and Discussion: We discovered that the new substances are characterized by a noticeable bathochromic shift of the absorption and emission maxima, as well as by a remarkable Stokes shift and a significant FQY variation depending on the properties of the medium. Conclusions: We designed a new series of arylidene-azolones with an extended system of conjugated bonds, that can be potentially applicable as fluorogenic dyes and polarity sensors.