Planar-Twisted Molecular Engineering for Modulating the Fluorescence Brightness of NIR-II Fluorophores with a Donor–Acceptor–Donor Skeleton

作者：Shiyang Ji, Yuying Du, Jiancai Leng, Yujin Zhang, Wei Hu · 发表于：International Journal of Molecular Sciences · 年份：2024 · DOI：10.3390/ijms252212365 · 被引用次数：5 · 研究领域：Luminescence and Fluorescent Materials、Nanoplatforms for cancer theranostics、Molecular Sensors and Ion Detection

Organic molecular fluorophores have been extensively utilized for biological imaging in the visible and the first near-infrared windows. However, their applications in the second near-infrared (NIR-II) window remain constrained, primarily due to the insufficient fluorescence brightness. Herein, we employ a theoretical protocol combining the thermal vibration correlation function with the time-dependent density functional theory method to investigate the mechanism of the planar-twisted strategy for developing fluorophores with balanced NIR-II emission and fluorescence brightness. Based on a planar donor–acceptor–donor molecular skeleton, various ortho-positioned alkyl side chains with steric hindrances are tactfully incorporated into the backbone to construct a series of twisted fluorophores. Photophysical characterizations of the studied fluorophores demonstrate that the emission spectra located in the NIR-II region exhibited a hypsochromic shift with the structural distortion. Notably, conformational twisting significantly accelerated the radiative decay rate while simultaneously suppressing the nonradiative decay rate, resulting in an improved fluorescence quantum efficiency (FQE). This enhancement can be mainly attributed to both the enlarged adiabatic excitation energy and reduced nonadiabatic electronic coupling between the first excited state and the ground state. Compared with the planar fluorophore, the twisted structures possessed a more than fivefold increase in FQE...