Design of Enaminitrile Switches with Enhanced Protofluorochromic Properties

Functional switches exhibiting distinct functionalities responding to a specific stimulus are highly desirable for fabricating advanced devices with superior dynamic performances. Herein, we explored a series of enaminitrile switches as protofluorochromic entities by modulation of their structures, assisted by DFT calculations. The switches show high stabilities, and exhibit reversible E/Z isomerization behavior, along with tunable fluorescence intensity in both protic and aprotic media. Switches based on 2-pyridyl- or 2-pyridylmethyl-containing N-components exhibited strong fluorescence in their protonated Z-configurations, compared to their phenyl/benzyl counterparts. This behavior could be attributed to variations in intramolecular charge transfer (ICT) or excited-state intramolecular proton transfer (ESIPT) effects. The Z-isomers were furthermore studied in their aggregated solid/film/dispersion states, resulting in notable aggregration-induced emission (AIE) behavior.