Spiropyrans (SPs) are an important group of photochromic compounds with a wide range of applications. In order to effectively design and utilize these photoswitches, it is necessary to understand how the photochromic properties are affected by substituents with different electron withdrawing or donating power, and solvents. In this work, the photophysical properties and mechanism of molecular switching in spiropyran derivatives SP-X_1-7 (X_1-7 = H, NO₂, CF₃, CN, OH, OMe and NMe₂) was investigated at GD3-TD-CAM-B3LYP/6-31 G(d) level of theory in the ground and excited states in the gas phase and three solvent media. According to obtained results, the energy barrier in the excited states was lower than that found in the ground state, showing that the process of photo-switching in the excited state is faster than the ground state. Our results showed that SP to merocyanine (MC) switching process could be divided into two steps: elongation of C_spiro−O distance to reach the cis-MC structure and, in turn, rotation around the central torsion angle to touch the trans-MC structure. The results showed that the first step is the rate-determining step of SP to trans-MC isomerization. In addition, solvent and substituent effects, photophysical properties, structural parameters, relative energies, and natural bond orbital (NBO) data were explored in detail.

螺吡喃（SP）是一组重要的光致变色化合物，具有广泛的应用范围。为了有效地设计和利用这些光开关，必须了解光致变色特性如何受到具有不同吸电子或供电能的取代基和溶剂的影响。在这项工作中，螺吡喃衍生物SP-X _1-7（X _1-7 = H，NO ₂，CF ₃，CN，OH，OMe和NMe ₂的光物理性质和分子转换机理）是在GD3-TD-CAM-B3LYP / 6-31 G（d）理论水平下在气相和三种溶剂介质中的基态和激发态下进行研究的。根据获得的结果，在激发态下的能垒比在基态下低，这表明在激发态下的光开关过程比基态快。我们的结果表明，SP转变为花青素（MC）的过程可以分为两个步骤：延长C_螺旋-O距离以达到顺式-MC结构，然后绕中心扭转角旋转以接触反式-MC结构体。结果表明：第一个步骤是的速率决定步骤SP到反式-MC异构化。此外，还详细探讨了溶剂和取代基效应，光物理性质，结构参数，相对能量和天然键轨道（NBO）数据。