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一、导论在地球这颗行星上,光诱导反应的存在显然比生命本身还要悠久。地球生长期后,一当劫灰初定,日光诱导的光化学就必定已实实在在地开始了。在最初的十亿年中,行星上开始产生氧气并建立起今日的大气层。同温层中氧气的光解产生了保护性的臭氧层,它屏障了人类和动物的生命使免受太阳光谱中高能成分的辐照,当人类脱落了遍身的体毛,日光的作用开始使人类DNA的胸腺嘧啶片段二聚化及诱发别的变化,导致皮肤癌。接着,人类的身体通过别的修复过程发展起光复活机能。所有这些光反应都是在没有人类的干涉或确切地说,在不被注意的情况下亘古地进行着。科学家最初是怎样意识到物质与光的相互作用不但能产生物理现象,如阴影、吸收、反射、衍射,而且还能改变它们的化学性质的呢?什么样的变化才足够引起化学家的注意呢?对当时的化学家来说,化学组成和外观是化学物质的主要特征,而“结构”的含义则基本未知。大量日光诱导的物质外观或其功能上的改变确实被注意到了,如纤维的脱色效应、油画的保存和屋外油漆的“白垩化”,啤酒的毒害效应、及火药棉的报废等。除了这些实用性的事例外,还有三种类型的变化能引起实验化学家的好奇心:即颜色改变,无论暂时性或永久性的;液体中气泡的产生;和溶解度小于前体的光产物的沉淀。
I. INTRODUCTION On the planet Earth, the existence of light-induced reactions is obviously longer than life itself. After the Earth’s growth period, when the ash-masters are set to begin, sunlight-induced photochemistry must have really started. In the first billions of years, oxygen began to build on the planets and build up today’s atmosphere. The photolysis of oxygen in the stratosphere produces a protective ozone layer that shields the lives of humans and animals from the high energy components of the sun’s spectrum. When humans shed their body hair, the sunlight begins to make humans Thymine DNA fragments dimerize and induce other changes, leading to skin cancer. Then, the human body develops light and resurrection functions through other repair processes. All these photoreactions are carried out without human intervention or, more precisely, without being noticed. How scientists first realized that the interaction of matter with light not only produces physical phenomena such as shading, absorption, reflection, diffraction, but also their chemical properties, and what changes are enough to arouse chemists’ attention For chemists of the time, chemistry and appearance were the main features of chemicals, while the meaning of “structure” was largely unknown. A lot of daylight-induced material appearance or functional changes are indeed noticed, such as the decoloring effect of fiber, painting preservation and outdoor paint “chalk”, the poisonous effect of beer, and gunpowder cotton scrap and so on. In addition to these practical examples, there are three other types of changes that are of interest to the experimental chemist’s curiosity: color change, whether temporary or permanent; bubble generation in liquids; and photolysis products less soluble than precursors precipitation.