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Two new acetoxyphenyl thiophenes with different conjugation length and undergoing the photo-Fries reaction upon exposure to UV light are presented. These molecules have been characterized in solution by means of different spectroscopic techniques in order to study the evolution and selectivity of the photo-induced reaction. During such a reaction, isosbestic points appear in the UV–vis spectra, indicating a good selectivity of the reaction for both the derivatives. By means of IR measurements, we follow the reaction and determine the kinetics and the quantum yield. The photoproducts are isolated by HPLC and characterized by 1H-NMR whose results confirm the formation of the ortho derivative as the most probable one and we estimate the degree of conversion of the reaction. High-level quantum mechanical calculations both in gas and solvated phase are employed to strongly support the interpretation of the experimental results, and assess the reaction product.