In this computational experiment, students use advanced quantum chemistry tools to simulate the photochromic reaction mechanism in naphthopyran derivatives. The first part aims to make students familiar with excited-state reaction mechanisms and addresses the photoisomerization of the benzopyran molecule by means of semiempirical quantum chemical calculations. This part introduces in particular the concept of conical intersection between potential energy surfaces and can be conducted under instructor guidance during a 4 h laboratory session. The second part investigates the photophysical and photochromic properties of two diphenyl-naphthopyran isomers and can be carried out independently by the students.