Annihilation Limit of a Visible-to-UV Photon Upconversion Composition Ascertained from Transient Absorption Kinetics
Annihilation Limit of a Visible-to-UV Photon Upconversion Composition Ascertained from Transient Absorption Kinetics
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DOI：
10.1021/jp4022618
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发表时间：
2013-05-30
影响因子：
2.9
通讯作者：
Castellano, Felix N.
中科院分区：
文献类型：
--
作者：
Deng, Fan;Blumhoff, Joerg;Castellano, Felix N.
利用八乙基卟啉钯（PdOEP）作为三重态敏化剂和蒽作为能量受体/湮灭剂，在真空脱气甲苯中实现了非相干敏化的绿光到近可见光的上转换。PdOEP的选择性547 nm激发与入射辐照度低至600 μ W/cm（2）的结果在较高能量的蒽基荧光观察。PdOEP被蒽动态磷光猝灭的Stern-Volmer分析具有极大的K-SV（810 000 M-1），得到三重态-三重态能量转移猝灭常数为3.3 × 10（9）M-1 s（-1）。大量的实验提供了蒽随后的三重态-三重态湮灭（TTA）的明确证据，其中最引人注目的是激发扫描，说明PdOEP的Q带吸收特征是唯一负责敏化反斯托克斯荧光。相对于激发功率的上转换的发射强度被示出为使用相干或非相干光源在二次和线性之间变化，说明了在连续波照明下产生光化学的光的预期动力学极限。在激光脉冲完全被样品吸收的条件下，直接比较通过上转换（λ（ex）= 547 nm，延迟信号）和直接激发（λ（ex）= 355 nm，即时信号）产生的总积分蒽强度/时间荧光数据的时间分辨实验显示约40%的湮灭效率。类似地，由施密特和同事报道的延迟荧光动力学分析（J. Phys. Chem. Lett. 2010，1，1795-1799）用于揭示来自模型红色至黄色上转换组合物的最大可能效率，并且将该处理应用于在430 nm处针对PdOEP/蒽组合物测量的蒽的蒽基三重态吸收衰减瞬变。从这个分析中，大约50%的蒽基三重态通过TTA衰变产生单线态荧光，这与湮灭自旋统计不对上转换光化学施加效率限制的概念一致。
Noncoherent sensitized green-to-near-visible upconversion has been achieved utilizing palladium(II) octaethylporphyrin (PdOEP) as the triplet sensitizer and anthracene as the energy acceptor/annihilator in vacuum degassed toluene. Selective 547 nm excitation of PdOEP with incident irradiance as low as 600 mu W/cm(2) results in the observation of anthryl fluorescence at higher energy. Stern-Volmer analysis of the dynamic phosphorescence quenching of PdOEP by anthracene possesses an extremely large K-SV of 810 000 M-1, yielding a triplet-triplet energy transfer quenching constant of 3.3 x 10(9) M-1 s(-1). Clear evidence for the subsequent triplet-triplet annihilation (TTA) of anthracene was afforded by numerous experiments, one of the most compelling was an excitation scan illustrating that the Q-band absorption features of PdOEP are solely responsible for sensitizing the anti-Stokes fluorescence. The upconverted emission intensity with respect to the excitation power was shown to vary between quadratic and linear using either coherent or noncoherent light sources, illustrating the expected kinetic limits for the light producing photochemistry under continuous wave illumination. Time-resolved experiments directly comparing the total integrated anthracene intensity/time fluorescence data produced through upconversion (lambda(ex) = 547 nm, delayed signal) and with direct excitation (lambda(ex) = 355 nm, prompt signal) under conditions where the laser pulse is completely absorbed by the sample reveal annihilation efficiencies of approximately 40%. Similarly, the delayed fluorescence kinetic analysis reported by Schmidt and co-workers (J. Phys. Chem. Lett. 2010, 1, 1795-1799) was used to reveal the maximum possible efficiency from a model red-to-yellow upconverting composition and this treatment was applied to the anthryl triplet absorption decay transients of anthracene measured for the PdOEP/anthracene composition at 430 nm. From this analysis approximately 50% of the anthryl triplets that decay by TTA produce singlet fluorescence, consistent with the notion that annihilation spin statistics does not impose efficiency limits on upconversion photochemistry.