Regulation and mechanisms of full-visible-spectrum emission in solid and liquid states for D-π-A cyanobenzene–phenothiazine fluorescent molecules

Abstract

The precise modulation of photophysical properties and elucidation of fluorescence mechanisms are paramount challenges for organic optoelectronic materials. Herein, we present a strategy for achieving robust fluorescence tuning from blue (462 nm) to near-infrared (677 nm) by accurately positioning electron-withdrawing groups relative to phenothiazine donors in cyanobenzene–phenothiazine derivatives, as well as adjusting molecular conformations, noncovalent interactions, and the interplays of aggregation behaviors. Crystallographic analysis and theoretical calculations revealed that 4-phenothiazino-isophthaliconitrile (4-PTZIPN) achieves both the highest solid-state fluorescence quantum yield (39.7%) and the longest fluorescence lifetime (1.26 µs) among the series, which is attributed to J-aggregation sustained by multiple intermolecular interactions. The conformation and rigidified non-canonical J-aggregation suppressed non-radiative decay pathways, leading to a significant increase in the quantum yield of 2,4,6-triphenothiazinobenzonitrile (1CN3PTZ) and a substantial extension of its fluorescence lifetime from 761.47 ns in the solid-state to 1.10 µs. Notably, 2,4,6-triphenothiazino-isophthaliconitrile (2CN3PTZ) demonstrates a pronounced bathochromic shift to 677 nm, driven by its helical columnar packing, which is orchestrated by cooperative π–π, dipole–dipole, and C–H⋯S interactions. This work not only elucidated the structure–photophysical relationships within the cyano-phenothiazine system but also provided a conformation-aggregation dual regulation strategy for the design of innovative organic optoelectronic materials through molecular engineering.