Singh-Rachford Tanya N, Castellano Felix N
Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
J Phys Chem A. 2008 Apr 24;112(16):3550-6. doi: 10.1021/jp7111878. Epub 2008 Mar 13.
Upconverted yellow singlet fluorescence from rubrene (5,6,11,12-tetraphenylnapthacene) was generated from selective excitation (lambdaex = 725 nm) of the red light absorbing triplet sensitizer palladium(II) octabutoxyphthalocyanine, PdPc(OBu)8, in vacuum degassed toluene solutions using a Nd:YAG/OPO laser system in concert with gated iCCD detection. The data are consistent with upconversion proceeding from triplet-triplet annihilation (TTA) of rubrene acceptor molecules. The TTA process was confirmed by the quadratic dependence of the upconverted delayed fluorescence intensity with respect to incident light, measured by integrating the corresponding kinetic traces as a function of the incident excitation power. In vacuum degassed toluene solutions, the red-to-yellow upconversion process is stable under continuous long wavelength irradiation and is readily visualized by the naked eye even at modest laser fluence (0.6 mJ/pulse). In aerated solutions, however, selective excitation of the phthalocyanine sensitizer leads to rapid decomposition of rubrene into its corresponding endoperoxide as evidenced by UV-vis (in toluene), 1H NMR (in d6-benzene), and MALDI-TOF mass spectrometry, consistent with the established reactivity of rubrene with singlet dioxygen. The upconversion process in this triplet sensitizer/acceptor-annihilator combination was preliminarily investigated in solid polymer films composed of a 50:50 mixture of an ethyleneoxide/epichlorohydrin copolymer, P(EO/EP). Films that were prepared under an argon atmosphere and maintained under this inert environment successfully achieve the anticipated quadratic incident power dependence, whereas air exposure causes the film to deviate somewhat from this dependence. To the best of our knowledge, the current study represents the first example of photon upconversion using a phthalocyanine triplet sensitizer, furthering the notion that anti-Stokes light-producing sensitized TTA appears to be a general phenomenon as long as proper energy criteria are met.
使用Nd:YAG/OPO激光系统并结合门控增强型电荷耦合器件（iCCD）检测，在真空脱气的甲苯溶液中，通过对吸收红光的三重态敏化剂八丁氧基酞菁钯（PdPc(OBu)8）进行选择性激发（λex = 725 nm），产生了来自红荧烯（5,6,11,12 - 四苯基萘并四苯）的上转换黄色单线态荧光。数据与红荧烯受体分子通过三重态 - 三重态湮灭（TTA）进行上转换的过程一致。通过对相应动力学曲线进行积分，测量上转换延迟荧光强度相对于入射光的二次依赖性，证实了TTA过程。在真空脱气的甲苯溶液中，红到黄的上转换过程在连续长波长照射下是稳定的，即使在适度的激光能量密度（0.6 mJ/脉冲）下也能用肉眼轻松观察到。然而，在通气溶液中，酞菁敏化剂的选择性激发导致红荧烯迅速分解为其相应的内过氧化物，这通过紫外 - 可见光谱（在甲苯中）、1H核磁共振（在氘代苯中）和基质辅助激光解吸电离飞行时间质谱（MALDI - TOF）得到证实，这与红荧烯与单线态氧的既定反应性一致。在由环氧乙烷/环氧氯丙烷共聚物P(EO/EP)的50:50混合物组成的固体聚合物薄膜中，对这种三重态敏化剂/受体 - 湮灭剂组合中的上转换过程进行了初步研究。在氩气气氛下制备并保持在这种惰性环境中的薄膜成功实现了预期的二次入射功率依赖性，而暴露在空气中会使薄膜在一定程度上偏离这种依赖性。据我们所知，当前的研究代表了使用酞菁三重态敏化剂进行光子上转换的首个实例，进一步支持了只要满足适当的能量标准，产生反斯托克斯光的敏化TTA似乎是一种普遍现象的观点。
