Exploring Emission Ratios: Influence of Neighboring Groups on TSAL Core

The photophysics of tris(salicylidenealdimines) (TSALs) has been examined, as they offer the possibility of populating multiple emissive species through the excited-state intramolecular proton transfer (ESIPT) reaction, resulting in broad visible spectrum coverage, a desirable property for white organic light-emitting diodes (wOLEDs). In this contribution, the synthesis and photophysical characterization of a new TSAL derivative, C16, are reported. It displays a distinct emission profile compared to previously studied tris(salicylideneanilines), with an inversion of the ESIPT/LE emission intensity ratio, exhibiting almost exclusively tautomer emission upon excitation in less polar solvents. Ab initio calculations suggest that the absence of emission from the locally excited (LE) state in nonpolar solvents may be related to the competition between two processes: ESIPT and N-pyramidalization of the enaminic nitrogen. Conversely, in polar aprotic solvents, the planar LE conformation is stabilized, and dual emission is observed. In protic solvents, however, the ESIPT reaction is suppressed due to competition with intermolecular hydrogen bonding interactions.