Grupo de Bioquímica Teórica, Universidad Industrial de Santander, Carrera 27, Calle 9, Bucaramanga, Colombia.
Phys Chem Chem Phys. 2015 May 7;17(17):11350-8. doi: 10.1039/c5cp00194c.
The effect of substituting the intra-cyclic sulphur of thionine by oxygen (oxonine) and selenium (selenine) on the intersystem crossing (ISC) efficiency has been studied using high level quantum mechanical methods. The ISC rate constants are considerably increased when going from O towards Se while the fluorescence rate constants remain unchanged. For the three dyes, all accessible ISC channels are driven by vibronic spin-orbit coupling (SOC) between ππ* states. The interplay between the ground and low-lying excited states has been investigated in order to determine the dominant relaxation pathways. In oxonine the relaxation to the ground state after photoexcitation in water proceeds essentially via fluorescence from the S1(πHπL*) bright state (kF = 2.10 × 10(8) s(-1)), in agreement with the high experimental fluorescence quantum yield. In aqueous solution of thionine, the ISC rate constant (kISC ∼ 1 × 10(9) s(-1)) is one order of magnitude higher than fluorescence (kF = 1.66 × 10(8) s(-1)) which is consistent with its high triplet quantum yield observed in water (ϕT = 0.53). Due to a stronger vibronic SOC in selenine, the ISC rate is very high (kISC ∼ 10(10) s(-1)) and much faster than fluorescence (kF = 1.59 × 10(8) s(-1)). This suggests selenine-based dyes as very efficient triplet photosensitizers.
用高精度量子力学方法研究了将硫堇中环的硫原子用氧（氧唪）和硒（硒唪）取代对系间穿越（ISC）效率的影响。当从 O 变为 Se 时，ISC 速率常数大大增加，而荧光速率常数保持不变。对于这三种染料，所有可及的 ISC 通道都由ππ态之间的振子轨道耦合（SOC）驱动。为了确定主要的弛豫途径，研究了基态和低激发态之间的相互作用。在氧唪中，在水中光激发后，弛豫到基态主要通过 S1（πHπL）亮态的荧光进行（kF = 2.10 × 10（8）s（-1）），这与高实验荧光量子产率一致。在硫堇的水溶液中，ISC 速率常数（kISC ∼ 1 × 10（9）s（-1））比荧光（kF = 1.66 × 10（8）s（-1））高一个数量级，这与其在水中观察到的高三重态量子产率（ϕT = 0.53）一致。由于硒唪中更强的振子 SOC，ISC 速率非常高（kISC ∼ 10（10）s（-1）），比荧光（kF = 1.59 × 10（8）s（-1））快得多。这表明基于硒唪的染料是非常有效的三重态光敏剂。
