Fabrication of efficient and red-emissive salicylaldehyde Schiff base isomers for multi-scenario information decryption

Abstract

Due to their broad applications in information technology, biochemical sensors, and optoelectronic devices, stimuli-responsive fluorescent materials (SRFMs) have gained significant attention. With their simple synthesis and modification, Schiff bases are considered promising candidates for SRFMs. However, realizing highly efficient luminescence with aggregation-induced emission (AIE) properties as well as stimuli responses is still challenging due to the lack of clear structure–property relationships. In this work, a general strategy for constructing efficient and red-emissive salicylaldehyde Schiff bases is proposed utilizing the triphenylamine (TPA) substitution strategy. Experimental results and theoretical calculations illustrate that all four isomers show a typical AIE effect of the keto-form emission upon photoexcitation and red fluorescence due to the charge-transfer transition from TPA on the salicylaldehyde unit to the keto unit. The single-crystal structure also demonstrates that the introduction of dual TPA leads to appropriate intermolecular interactions, resulting in high-intensity fluorescence. Moreover, with excellent acidochromic properties under both daylight and UV light conditions, p,p-2TPA is successfully applied in steganography and multi-scenario information decryption. This work not only realizes efficient and red-colored luminescence from a simple salicylaldehyde Schiff base skeleton but also provides a strategy for constructing SRFMs with AIE properties.