北京化工大学马志勇团队报道了激发态质子转移下双分子内氢键对聚合依赖性聚合物光致变色的影响。相关研究成果发表在2025年1月16日出版的《中国化学》。

激发态分子内质子转移（ESIPT）涉及两个激发态（E*和K*）之间通过分子内质子传递的光化学互变异构。基于有机ESIPT分子的光化学互变异构开发聚合物光致变色的报道很少。

该文中，研究人员报道了ESIPT分子HBT-2OH在聚氨酯（PU）网络中，表现出浓度依赖性的光致变色行为。在低浓度下，HBT-2OH主要以反式烯醇构型存在，PU中没有分子内OH··N氢键，在~464nm处发出蓝色荧光（烯醇发射）。在紫外线照射下，质子供体和受体之间的二面角扭曲形成分子内OH··N氢键，将反式烯醇转化为顺式烯醇，导致ESIPT在~603 nm处发出淡黄色荧光（酮发射）。

光致变色效应HBT-2OH@PU控制分子HBT、HBO-2OH和HBI-2OH在PU中没有表现出光致变色性，证实了乙醇支链和分子内OH···S氢键稳定了HBT-2OH的反式烯醇构型。将这些分子掺入PMMA和PCL网络表明，自由体积的增加和较小的聚集体，通过降低二面角扭曲的阻力来增强光致变色性。密度泛函理论（DFT）计算进一步证实了，HBT-2OH中存在稳定的分子内杂原子氢键（OH···S）。

该研究为聚合物基光致变色材料的研究提供了新的理论见解，开辟了新的途径。

附：英文原文

Title: Aggregation-Dependent Polymer Photochromism via Double Intramolecular Hydrogen Bonds from Excited State Intramolecular Proton Transfer

Author: Jingyuan Zhou, Huan Hu, Mingzhi Chen, Yongjie Li, Xin Cheng, Zhimin Ma, Shui Hu, Zhiyong Ma

Issue&Volume: 2025-01-16

Abstract: Excited-state intramolecular proton transfer (ESIPT) involves photochemical tautomerization between two excited states (E* and K*) via intramolecular proton transfer. Developing polymer photochromism based on the photochemical tautomerization of organic ESIPT molecules has been rarely reported. We report the ESIPT molecule HBT-2OH exhibits concentration-dependent photochromic behavior in a polyurethane (PU) network. At low concentrations, HBT-2OH primarily exists in the trans-enol configuration without intramolecular OH···N hydrogen bonds in PU, emitting blue fluorescence at ~464 nm (enol emission). Upon UV irradiation, the dihedral angle between the proton donor and acceptor twists to form an intramolecular OH···N H-bond, converting trans-enol to cis-enol and resulting in ESIPT with pale yellow fluorescence at ~603 nm (keto emission). The photochromic effect of HBT-2OH@PU diminishes at high concentrations due to that aggregation favors the cis-enol form. Control molecules HBT, HBO-2OH, and HBI-2OH show no photochromism in PU, confirming that ethanolyl branches and intramolecular OH···S hydrogen bonds stabilize the trans-enol configuration of HBT-2OH. Incorporating these molecules into PMMA and PCL networks demonstrates that increased free volume and smaller aggregates enhance photochromism by reducing resistance to dihedral angle twisting. Density functional theory (DFT) calculations further confirm stable intramolecular heteroatomic hydrogen bonds (OH···S) exist in HBT-2OH. This study offers new theoretical insights and opens avenues for research on polymer based photochromic materials.

DOI: 10.1002/cjoc.202401035

Source: https://onlinelibrary.wiley.com/doi/full/10.1002/cjoc.202401035