Photoacids undergo an increase in acidity upon electronic excitation, enabling excited-state proton transfer (ESPT) reactions. A multitude of compounds that allow ESPT has been identified and integrated in numerous applications, as is outlined by reviewing the rich history of photoacid research reaching back more than 90 years. In particular, achievements together with ambitions and challenges are highlighted from a combined experimental and theoretical perspective. Besides explicating the spectral signatures, transient ion-pair species, and electronic states involved in an ESPT, special emphasis is put on the diversity of methods used for studying photoacids as well as on the effects of the environment on the ESPT, illustrated in detail for 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) and the naphthols as examples of prototypical photoacids. The development of exceptionally acidic super-photoacids and magic photoacids is subsequently discussed, which opens the way to applications even in aprotic solvents and provides additional insight into the mechanisms underlying ESPT. In the overview of highlights from theory, a comprehensive picture of the scope of studies on HPTS is presented, along with the general conceptualization of the electronic structure of photoacids and approaches for the quantification of excited-state acidity. We conclude with a juxtaposition of established applications of photoacids together with potential open questions and prospective research directions.

中文翻译：

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ESPT 光酸的实验-理论双重视角及其未来的挑战


光酸在电子激发时酸度增加，从而能够发生激发态质子转移 （ESPT） 反应。正如回顾可追溯到 90 多年的光酸研究的丰富历史所概述的那样，已经确定并集成到许多应用中。特别是，从实验和理论相结合的角度突出了成就、抱负和挑战。除了阐明 ESPT 中涉及的光谱特征、瞬态离子对种类和电子状态外，还特别强调了用于研究光酸的方法的多样性以及环境对 ESPT 的影响，详细说明了 8-羟基芘-1,3,6-三磺酸盐 （HPTS） 和萘脑作为原型光酸的例子。随后讨论了异常酸性超光酸和神奇光酸的开发，这为即使在非质子溶剂中的应用开辟了道路，并为 ESPT 的潜在机制提供了额外的见解。在理论亮点概述中，全面介绍了 HPTS 的研究范围，以及光酸电子结构和激发态酸度定量方法的一般概念化。最后，我们将光酸的既定应用与潜在的开放问题和前瞻性研究方向并列。