Protofluorochromic enaminitrile molecular switches exhibit tunable fluorescence through E/Z isomerization and protonation. This study explores the influence of pyridine substitution on fluorescence properties, intramolecular charge transfer, and solvent-dependent behavior, offering insights into designing responsive optical materials.

Functional switches exhibiting distinct functionalities responding to a specific stimulus are highly desirable for fabricating advanced devices with superior dynamic performances. Herein, a series of enaminitrile switches are explored as protofluorochromic entities by modulation of their structures, assisted by density functional theory 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 exhibit strong fluorescence in their protonated Z-configurations, compared to their phenyl/benzyl counterparts. This behavior can be attributed to variations in intramolecular charge transfer or excited-state intramolecular proton transfer effects. The Z-isomers are furthermore studied in their aggregated solid/film/dispersion states, resulting in notable aggregation-induced emission behavior.