There is current interest in developing photoactive materials that deform on illumination. The strategy is to develop new photoactive molecules in solution, and then to incorporate these in the solid-state either by crystallization or by inserting them into polymers. This letter shows that the kinetics and the nature of the photo-induced phase transitions are profoundly different in single molecules (solution) and in the solid state using a lattice spin model. In solution, where the molecules act independently, the photoreaction follows first-order kinetics. However, in the solid state where the photoactive molecules interact with each other and therefore behave collectively during reaction, photoreactions follow the sigmoidal kinetics of nucleation and growth as in a first-order phase transition. Further, we find that the exact nature of the photo-induced strain has a critical effect on the kinetics, equilibrium, and microstructure formation. These predictions agree qualitatively with experimental observations, and provide insights for the development of new photoactive materials.

当前对开发在光照下变形的光敏材料感兴趣。该策略是在溶液中开发新的光敏分子，然后通过结晶或将其插入聚合物中将其掺入固态。这封信表明，使用晶格自旋模型，在单分子（溶液）和固态下，光诱导相变的动力学和性质有很大不同。在溶液中，分子独立起作用，光反应遵循一级动力学。然而，在固态中，光活性分子彼此相互作用，因此在反应过程中共同起作用，光反应遵循成核和生长的S形动力学，就像在一阶相变中一样。进一步，我们发现，光致应变的确切性质对动力学，平衡和微结构的形成具有至关重要的影响。这些预测在质量上与实验观察相符，并为开发新型光敏材料提供了见识。