Cao Jianfang, Chen Xinyu, Ma Xue, Zhang Tianci, Sun Wen
School of Chemical Engineering, Ocean and Life Sciences, Dalian University of Technology, Panjin Campus, Panjin, 124221, China.
State Key Laboratory of Fine Chemicals, Dalian University of Technology, No. 2 Linggong Road, High-tech District, Dalian, 116024, China.
Phys Chem Chem Phys. 2024 Aug 14;26(32):21520-21529. doi: 10.1039/d4cp01346h.
As a class of photosensitizers (PSs) with dual functions of photodynamic therapy (PDT) and fluorescence imaging, the relationship between the structure and dual-function of thiophene-fused-type BODIPY dyes has not been studied in depth before. We found that the thiophene-fused-type BODIPY triplet photosensitizer is produced according to the energy level matching rule and the introduction of the thiophene ring significantly reduces the energy gap Δ between singlet and triplet states, as revealed by our investigation of the excited state structures and energies of thieno-fused BODIPY dyes. At the same time, a tiny Δ also results in a greatly enhanced intersystem crossing (ISC) rate, . The value of MeO-BODIPY, having the highest singlet oxygen quantum yield (), is the largest. Substitution with a strong electron donor ,-dimethylaminophenyl (DMA) leads to the vertical configuration in the T state. The small Δ (0.0029 eV) between the HOMO and HOMO-1 triggers the photo induced electron transfer (PET) of inhibiting ISC and fluorescence. When thieno-fused BODIPYs react with pyrrole, the increase of π-conjugation and smaller Δ explain the redshift in emission wavelength of thieno-pyrrole-fused BODIPY. The more planar configuration of the S state and the stronger oscillator intensity reflect a higher fluorescence quantum yield (). The extension of π-conjugation can cause molecules to transition to higher-level singlet excited states (S states, ≥ 1) after absorbing energy and reduce the energy level of the excited state, resulting in multiple channels and favoring O production for thieno-pyrrole-fused BODIPYs with electron-withdrawing groups at the -position of the phenyl groups. Due to Δ < 0.980 eV, the substitution of electron-donating groups cannot produce O. In this work, we have revealed the mechanism of ISC and the fluorescence emission process in the thiophene-fused-type BODIPY dye, which has provided a theoretical foundation and guidance for the future design of BODIPY-based heavy-atom-free PSs for molecular applications in PDT.
作为一类具有光动力疗法（PDT）和荧光成像双重功能的光敏剂（PSs），噻吩稠合型BODIPY染料的结构与双重功能之间的关系此前尚未得到深入研究。我们发现，噻吩稠合型BODIPY三重态光敏剂是根据能级匹配规则产生的，并且噻吩环的引入显著降低了单重态和三重态之间的能隙Δ，这在我们对噻吩稠合BODIPY染料的激发态结构和能量的研究中得到了揭示。同时，微小的Δ也导致系间窜越（ISC）速率大大提高。具有最高单线态氧量子产率（）的MeO - BODIPY的 值最大。用强电子给体，-二甲基氨基苯基（DMA）取代会导致T态的垂直构型。HOMO和HOMO - 1之间小的Δ（0.0029 eV）引发抑制ISC和荧光的光诱导电子转移（PET）。当噻吩稠合的BODIPY与吡咯反应时，π共轭的增加和更小的Δ解释了噻吩 - 吡咯稠合BODIPY发射波长的红移。S态更平面的构型和更强的振子强度反映了更高的荧光量子产率（）。π共轭的扩展会使分子在吸收能量后跃迁到更高能级的单重激发态（S态，≥1），并降低激发态的能级，导致多种途径，有利于在苯基 - 位带有吸电子基团的噻吩 - 吡咯稠合BODIPY产生单线态氧。由于Δ<0.980 eV，给电子基团的取代不能产生单线态氧。在这项工作中，我们揭示了噻吩稠合型BODIPY染料中ISC和荧光发射过程的机制，这为未来设计用于PDT分子应用的基于BODIPY的无重原子PSs提供了理论基础和指导。
