Two New Multifunctional Hydrogen-Bonded Supramolecular Compounds Based on Viologen: Photochromism, Photocontrolled Fluorescence, and Ammonia Detection

Two novel viologen-functionalized Supramolecular compounds {[H₂bpybc]_0.5⋅[H₂BTEC]_0.5⋅ H₂O}_n (1) and {[H₂bpybc]⋅[H₃BTEC]₂⋅2H₂O}_n (2), were synthesized through a solution-based approach in the presence of 1,1'-bis((4-carboxybenzyl)-4,4'-bipyridine) chloride (H₂bpybc⋅2Cl), 1,2,4,5-benzenetetracarboxylic acid (H₄BTEC), and Zn(NO₃)₂⋅6H₂O. Single crystal X-ray diffraction analysis showed the three-dimensional supramolecular network structures within compounds 1 and 2. Notably, these compounds exhibit reversible photochromism due to the formation of viologen radicals, facilitating electron transfer. The order of light response time follows the sequence 1 > 2. To further elucidate the discoloration mechanism, Time dependent density functional theory (TDDFT) was employed. Additionally, compound 1 showed interesting photomodulated fluorescence behavior. Faster responsive rate is observed in the system of 1 due to its shorter D–A distance and intramolecular hydrogen bonding structure. Remarkably, compound 1 displays selective sensing capabilities towards NH₃ and triethylamine among various organic amines. Given its photochromic properties, compound 1 holds promise as a potential candidate for photochromic materials, anti-counterfeit paints, and information monitoring technology applications.