Merocyanine–spiropyran relaxation processes Olha Kovalenko, Yuriy Lopatkin, Petro Kondratenko and Dmitro Belous Eur. Phys. J. D, 72 1 (2018) 20 Published online: 25 January 2018 DOI: 10.1140/epjd/e2017-80306-4