Wei Zimu, Sharma Sushil, Philip Abbey M, Sengupta Sanchita, Grozema Ferdinand C
Department of Chemical Engineering, Delft University of Technology, Delft, The Netherlands.
Phys Chem Chem Phys. 2021 Apr 14;23(14):8900-8907. doi: 10.1039/d1cp00453k. Epub 2021 Apr 6.
Donor-bridge-acceptor systems based on boron dipyrromethene (BODIPY) are attractive candidates for bio-imagining and sensing applications because of their sensitivity to temperature, micro-viscosity and solvent polarity. The optimization of the properties of such molecular sensors requires a detailed knowledge of the relation between the structure and the photophysical behavior in different environments. In this work we have investigated the excited-state dynamics of three acceptor-donor-acceptor molecules based on benzodithiophene and BODIPY in solvents of different polarities using a combination of ultrafast spectroscopy and DFT-based electronic structure calculations. Transient absorption spectra show that upon photoexcitation an initial excited species with an induced absorption band in the near-infrared regime is formed independent of the solvent polarity. The subsequent photophysical processes strongly depend on the solvent polarity. In non-polar toluene this initial excited state undergoes a structural relaxation leading to a delocalized state with partial charge transfer character, while in the more polar tetrahydrofuran a fully charge separated state is formed. The results clearly show how factors such as donor-acceptor distance and restricted rotational motion by steric hindrance can be used to tune the excited state photophysics to optimize such systems for specific applications.
基于硼二吡咯亚甲基（BODIPY）的供体-桥-受体体系因其对温度、微粘度和溶剂极性的敏感性，成为生物成像和传感应用的有吸引力的候选者。优化此类分子传感器的性能需要详细了解其在不同环境中的结构与光物理行为之间的关系。在这项工作中，我们结合超快光谱和基于密度泛函理论（DFT）的电子结构计算，研究了三种基于苯并二噻吩和BODIPY的受体-供体-受体分子在不同极性溶剂中的激发态动力学。瞬态吸收光谱表明，光激发后会形成一种在近红外区域具有诱导吸收带的初始激发物种，且该物种的形成与溶剂极性无关。随后的光物理过程强烈依赖于溶剂极性。在非极性甲苯中，这种初始激发态会经历结构弛豫，导致形成具有部分电荷转移特征的离域态，而在极性更强的四氢呋喃中，则会形成完全电荷分离态。结果清楚地表明，诸如供体-受体距离和空间位阻引起的受限旋转运动等因素，可如何用于调节激发态光物理性质，从而针对特定应用优化此类体系。
