Design and Synthesis of Photoswitchable Conjugated Dithienylethene-Naphthalimide Scaffolds: Applications in Molecular Logic and Anticounterfeiting

Modulation of optical properties by multiple stimuli became a valuable tool to design molecular switching devices, logic gates, sensing devices, advanced anti-counterfeiting agents, etc. Herein, a dithienylethene (DTE)-, naphthalimide (NI)-, and aniline-based molecular switch was conceptually designed and synthesized, which showed efficient fluorescence switching by light irradiation, as well as acid/base stimuli. The switching of fluorescence was carried out by modulation of photoinduced electron transfer (PET) and energy transfer mechanisms. Feasibility of the PET process was further corroborated by calculating Gibb's free energy following the Rehm-Weller equation as well as by computational calculations. The molecule showed visible-light (400 nm)-triggered photocyclization, which was further validated by its congeners with various electron-donating as well as electron-withdrawing substituents. The multifunctional fluorescence switching capability of the compound was utilized to develop a complex logic gate, where UV light, visible light, acid, and base were used as external stimuli as input function. The compounds showed a substitution-dependent fluorescence switching ratio, where the 4-benzonitrile-based compound had the highest fluorescence switching ratio among all congeners (4-benzonitrile, phenyl, aniline, and anisole) and was utilized to generate photochromic and fluorescent patterns and write secret code.