太阳光中的紫外线能造成地球上的动植物不同程度的光损伤。防晒剂的使用已成为减少和防止皮肤光损伤的一种重要手段。近来，化学防晒剂分子的光物理和光化学过程引起了实验学家的广泛研究，但其微观机制仍不清楚，特别是在溶液中的光保护机制。目前的理论研究主要研究气相的微观机制，考虑环境效应的防晒霜分子的光保护机理很少报道。该项目拟采用高精度的量子力学/分子力学(QM/MM)激发态电子结构计算方法系统地研究一系列防晒剂分子在不同溶剂环境中的激发态特性、光物理、和光化学机理，包括取代基对激发态失活途径的影响等。研究工作不仅有助于弄清楚化学防晒剂分子的光保护的微观机制，还为理性设计性能更加优越、更加安全的新型化学防晒剂提供重要的理论参考。

Ultraviolet radiation of solar spectrum can cause photodamage in varying degrees to animals and plants on Earth. The use of sunscreens has now become an important means of reducing and preventing photodamage to the skin. Recently, the photophysical and photochemical processes of chemical sunscreen molecules have led to extensively research by experimentalists, but their microscopic mechanisms are still unclear, especially the photoprotection mechanisms in solution. The previous theoretical studies mainly focused on microscopic mechanisms in gas phase, and photoprotection mechanisms of sunscreen molecules with consideration of environment effects were rarely reported. The present project intends to systematically investigate the excited-state properties, photophysical and photochemical mechanisms of a series of sunscreen molecules in different solvent environments, including effects of substituent groups on excited-state decay pathways, using high level quantum mechanics/molecular mechanics (QM/MM) excited-state electronic structure calculations. The research not only helps clarify the microscopic photoprotection mechanisms of chemical sunscreen molecules, but also provides important theoretical references for the rational design of new and superior chemical sunscreens.