State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, E-208 West Campus, 2 Ling Gong Road, Dalian 116024, China.
Phys Chem Chem Phys. 2021 Apr 14;23(14):8641-8652. doi: 10.1039/d1cp00948f. Epub 2021 Mar 29.
The photophysical properties of a heavy atom-free BODIPY derivative with a twisted π-conjugated framework were studied. Efficient intersystem crossing (ISC quantum yield: 56%) and an exceptionally long-lived triplet state were observed (4.5 ms in solid polymer film matrix and 197.5 μs in solution). Time-resolved electron paramagnetic resonance (TREPR) spectroscopy and DFT computations confirmed the delocalization of the triplet state on the whole twisted π-conjugated framework and the zero-field-splitting (ZFS) D parameter of D = -69.5 mT, which is smaller than that of 2,6-diiodoBODIPY (D = -104.6 mT). The electron spin polarization (ESP) phase pattern of the triplet state TREPR spectrum of the twisted BODIPY is (a, a, e, a, e, e), which is different from that of 2,6-diiodo BODIPY (e, e, e, a, a, a), indicating that the electron spin selectivity of the ISC of the twisted structure is different from that of the spin orbital coupling effect. According to the computed spin-orbit coupling matrix elements (0.154-1.964 cm), together with the matched energy of the S/T states, ISC was proposed to occur via S→T/T. The computational results were consistent with TREPR results on the electron spin selectivity (the overpopulation of the T sublevel of the T state). The advantage of the long-lived triplet state of the twisted BODIPY was demonstrated by its efficient singlet oxygen (O) photosensitizing (Φ = 50.0%) even under a severe hypoxia atmosphere (pO = 0.2%, v/v). A high light toxicity (EC = 1.0 μM) and low dark toxicity (EC = 78.5 μM) were observed for the twisted BODIPY, and thus the cellular studies demonstrate its potential as a novel potent heavy atom-free photodynamic therapy (PDT) agent.
研究了具有扭曲π共轭骨架的无重原子 BODIPY 衍生物的光物理性质。观察到有效的系间窜越（ISC 量子产率：56%）和异常长寿命的三重态（在固体聚合物膜基质中为 4.5 毫秒，在溶液中为 197.5 微秒）。时间分辨电子顺磁共振（TREPR）光谱和 DFT 计算证实了三重态在整个扭曲的π共轭骨架上的离域和零场分裂（ZFS）D 参数 D = -69.5 mT，小于 2,6-二碘 BODIPY（D = -104.6 mT）。扭曲 BODIPY 的三重态 TREPR 光谱的电子自旋极化（ESP）相位图案为（a，a，e，a，e，e），与 2,6-二碘 BODIPY 的不同（e，e，e，a，a，a），表明扭曲结构的 ISC 的电子自旋选择性与自旋轨道耦合效应不同。根据计算的自旋轨道耦合矩阵元（0.154-1.964 cm），以及 S/T 态的匹配能量，ISC 被提出通过 S→T/T 发生。计算结果与 TREPR 对电子自旋选择性的结果一致（T 态 T 亚能级的过占）。扭曲 BODIPY 的长寿命三重态的优势通过其在严重缺氧气氛（pO = 0.2%，v/v）下有效的单线态氧（O）光敏化（Φ=50.0%）得到证明。扭曲 BODIPY 表现出高光毒性（EC = 1.0 μM）和低暗毒性（EC = 78.5 μM），因此细胞研究表明其作为新型强效无重原子光动力疗法（PDT）药物具有潜力。
