Computational Study on the Substituent Group, Positions and <i>Cis/Trans</i> ‐Isomerism Impact of Azobenzene‐Based Photoresponsive Ionic Liquids

ABSTRACT Azobenzene‐based photoresponsive ionic liquids (ILs) exhibit unique light‐modulated properties, yet the structural determinants of their isomerization and aggregation remain underexplored. Density functional theory (DFT) calculations were employed to systematically investigate the substituent effects, positions and cis/trans ‐isomerism of azobenzene‐functionalized ILs ([XAzoC 2 DMEA]Br, X = CH 3 /CN/NH 2 /NO 2 /OCH 3 /OH). Key findings reveal that substituent electronic nature and positional isomerism critically regulate electrostatic potential (ESP) distribution, molecular volume, and hydrogen bond strength. Electron‐withdrawing groups (CN, NO 2 ) enhance anion‐cation interactions by intensifying charge polarization, whereas electron‐donating groups (NH 2 , OCH 3 ) reduce interaction energies through electron density redistribution. Para‐substituted trans ‐isomers demonstrate enhanced thermodynamic stability owing to optimized conjugation effects and minimized steric hindrance. Hydrogen bond networks stabilize ionic pairs, with Br − forming multiple interactions. Cluster analysis reveals cooperative stabilization in multi‐ion aggregates, with cis ‐clusters achieving marginally stronger interactions at larger sizes due to adaptive hydrogen‐bond networks. Electrostatic forces dominate ILs stabilization, while hydrogen bonds modulate dynamic aggregation processes. These insights advance the molecular‐level design of photoresponsive ILs for applications in sensors, photo‐switchable devices, and sustainable chemistry.