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Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
Substituent-triggered cross-phase inversion of excimer formation
Hua Zhao1, Jinshan Xu1, Wei Chen1
1College of Chemistry and Chemical Engineering, Nanchang University, Nanchang 330031, China.
Abstract:
Excimer formation is governed by distinct dynamic and static mechanisms in solution and crystalline states, yet their intrinsic correlation remains poorly understood. Here we report a striking substituent-triggered cross-phase inversion of excimer formation in a series of acridine derivatives. In solution, unsubstituted acridine (AD-H) and 9-phenylacridine (AD-Ph) readily form dynamic excimers at elevated concentrations, whereas the 2-methoxy-substituted analogue (AD-Ph-OMe) exhibits exclusively monomeric emission due to steric hindrance and enhanced hydrogen-bonded solvation. In the crystalline state, this trend is fully reversed: AD-Ph-OMe self-assembles into discrete slipped face-to-face dimers (dπ-π = 3.481 Å and Sπ-π = 90.2%), preorganized by directional Ar-H···O interactions, giving rise to intense excimer emission at ∼494 nm with a high photoluminescence quantum yield of 64.8%, while AD-Ph shows only partial excimer contribution and AD-H exhibits none. This study highlights how subtle substituent modulation can invert excimer propensity across phases, providing molecular-level insight into aggregation-controlled photophysics and the design of discrete excimer emitters.
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