Deng Fan, Sun Wenfang, Castellano Felix N
Department of Chemistry, North Carolina State University, Raleigh, NC 27695-8204, USA.
Photochem Photobiol Sci. 2014 May;13(5):813-9. doi: 10.1039/c4pp00037d.
Near-IR (NIR) absorption from a Cd(ii) texaphyrin (TXP) has been successfully coupled with rubrene triplet acceptors/annihilators in vacuum degassed dichloromethane to upconvert NIR (670-800 nm) incident photons into yellow fluorescence through sensitized triplet-triplet annihilation. Stern-Volmer analysis of dynamic energy transfer quenching of TXP by rubrene using transient absorption spectroscopy revealed Stern-Volmer and bimolecular quenching constants of 21,000 M(-1) and 5.7 × 10(8) M(-1) s(-1) respectively, for the triplet-triplet energy transfer process. The upconverted emission intensity with respect to the incident excitation power density at 750 nm was shown to vary between quadratic and linear, illustrating the expected kinetic limits for the light producing photochemistry under continuous wave illumination. Furthermore, with increasing TXP sensitizer concentration, the characteristic quadratic-to-linear crossover point shifted to lower incident photon power density. This is consistent with the notion that stronger photon capture in the sensitizer leads to experimental conditions promoting upconversion under milder excitation conditions. The maximum quantum yield of the TXP-sensitized rubrene upconverted fluorescence was 1.54 ± 0.04% under dilute conditions determined relative to Os(phen)32 under continuous wave excitation conditions. This saturating quantum efficiency was realized when the incident light power dependence reached the quadratic-to-linear crossover point and was constant over the region where the composition displayed linear response to incident light power density. In pulsed laser experiments at higher sensitizer concentrations, the triplet-triplet annihilation quantum yield was determined to saturate at approximately 13%, corresponding to an upconversion yield of ∼10%, suggesting that the dichloromethane solvent either lowers the T2 state of the rubrene acceptor or is somehow attenuating the annihilation reaction between excited rubrene triplets.
在真空脱气的二氯甲烷中，已成功将镉（II） texaphyrin（TXP）的近红外（NIR）吸收与红荧烯三重态受体/湮灭剂耦合，通过敏化三重态-三重态湮灭将近红外（670-800 nm）入射光子上转换为黄色荧光。使用瞬态吸收光谱对红荧烯对TXP的动态能量转移猝灭进行的斯特恩-沃尔默分析表明，三重态-三重态能量转移过程的斯特恩-沃尔默猝灭常数和双分子猝灭常数分别为21,000 M⁻¹和5.7×10⁸ M⁻¹ s⁻¹。相对于750 nm处的入射激发功率密度，上转换发射强度在二次方和线性之间变化，说明了连续波照射下产生光化学的预期动力学极限。此外，随着TXP敏化剂浓度的增加，特征性的二次方到线性的交叉点移至更低的入射光子功率密度。这与以下观点一致，即敏化剂中更强的光子捕获导致在更温和的激发条件下促进上转换的实验条件。在连续波激发条件下，相对于Os(phen)₃₂，在稀释条件下TXP敏化的红荧烯上转换荧光的最大量子产率为1.54±0.04%。当入射光功率依赖性达到二次方到线性的交叉点并且在组合物对入射光功率密度显示线性响应的区域内恒定时，实现了这种饱和量子效率。在更高敏化剂浓度的脉冲激光实验中，三重态-三重态湮灭量子产率被确定在约13%时达到饱和，对应于约10%的上转换产率，这表明二氯甲烷溶剂要么降低了红荧烯受体的T2态，要么以某种方式减弱了激发的红荧烯三重态之间的湮灭反应。
