Sun Bingqing, Liu Lei, Yoon Juyoung
College of Resource and Environment, Anhui Science and Technology University, Fengyang 233100, China.
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116000, China.
J Phys Chem A. 2025 Mar 13;129(10):2420-2428. doi: 10.1021/acs.jpca.4c07483. Epub 2025 Feb 26.
Schiff base with a C═N bond is widely used in the fabrication of turn-on sensors for cations. The isomerization of C═N is generally believed to induce a dark state and quenches the sensor's fluorescence. With the aid of time-dependent density functional theory (TDDFT), this contribution performs a comprehensive investigation on the photophysical process of a turn-on sensor for Al. The isomerization of C═N leads to a non-emissive twisted intramolecular charge transfer (TICT) state, which is initiated by an early stage excited state intramolecular proton transfer (ESIPT) process. However, this isomerization process has a very large energy barrier and low reaction rate that cannot effectively quench the sensor's fluorescence. Interestingly, a brand new non-emissive TICT state is observed which is not induced by the isomerization of C═N but by the rotation of a neighboring C-C bond. Due to the low rotation energy barrier, this new TICT state can be attained easily and opens up an effective channel for non-emissive decays. This observation implies that the excited state potential energy surface for sensors based on a Schiff base should be much more complicated than expected. Based on the photophysical process, the sensing mechanism for Al as well as its selectivity in the face of interfering cations are uncovered.
具有C═N键的席夫碱被广泛用于制造阳离子开启型传感器。一般认为C═N的异构化会诱导暗态并淬灭传感器的荧光。借助含时密度泛函理论（TDDFT），本论文对一种铝离子开启型传感器的光物理过程进行了全面研究。C═N的异构化导致非发射性的扭曲分子内电荷转移（TICT）态，该态由早期激发态分子内质子转移（ESIPT）过程引发。然而，这种异构化过程具有非常大的能垒和低反应速率，无法有效淬灭传感器的荧光。有趣的是，观察到一种全新的非发射性TICT态，它不是由C═N的异构化而是由相邻C-C键的旋转诱导产生的。由于旋转能垒较低，这种新的TICT态很容易形成，并为非发射性衰减开辟了一条有效通道。这一观察结果表明，基于席夫碱的传感器的激发态势能面应比预期的复杂得多。基于光物理过程，揭示了铝离子的传感机制及其在面对干扰阳离子时的选择性。
