There has been an increasing amount of interest in stepwise two-photon-absorption (2PA)-induced photochemical reactions because of their extremely lower power thresholds compared to that of the simultaneous process and drastic reaction enhancements in some cases. However, stepwise 2PA-induced photochemical reactions were reported only in single chromophores and covalently bound bichromophores and there are few reports on these reactions in noncovalently bound systems because of weak electronic interactions among chromophores. This study demonstrated the stepwise 2PA-induced electron transfer from higher excited states in noncovalently bound protoporphyrin IX·CdS/ZnS core/shell nanocrystals (NCs). The electron transfer from higher excited states of porphyrin to CdS NCs successfully overcomes the activation barrier associated with the wide bandgap ZnS shell, indicating that a high reduction potential can be obtained with the stepwise 2PA process. The concept presented in this study can be applied to various noncovalently bound multichromophore systems to explore nonlinear photoresponses.

中文翻译：

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非共价结合卟啉-CdS / ZnS核/壳纳米晶体高激发态的逐步双光子诱导电子转移

在逐步的双光子吸收（2PA）诱导的光化学反应中，人们越来越感兴趣，因为与同时进行的过程相比，它们的功率阈值极低，在某些情况下，反应的剧烈增强。然而，仅在单个生色团和共价结合的双生色团中报道了逐步2PA诱导的光化学反应，由于生色团之间的弱电子相互作用，在非共价结合的系统中关于这些反应的报道很少。这项研究证明了在非共价结合的原卟啉IX·CdS / ZnS核/壳纳米晶体（NCs）中，2PA诱导的电子从较高的激发态转移。从卟啉高激发态到CdS NCs的电子转移成功克服了宽带隙ZnS壳层相关的活化势垒，表明逐步2PA工艺可获得高还原电位。本研究中提出的概念可以应用于各种非共价结合的多发色团系统，以探索非线性光响应。