ARTICLE pubs.acs.org/JPCA
Ultrafast Ring-Opening/Closing and Deactivation Channels for a Model SpiropyranMerocyanine System Marta Sanchez-Lozano,† Carlos Manuel Estevez,*,† Jose Hermida-Ramon,† and Luis Serrano-Andres‡ † ‡
Departamento de Química Física, Facultade de Química, Universidade de Vigo, 36310 Vigo, Spain Instituto de Ciencia Molecular, Universitat de Valencia, 46071 Valencia, Spain
bS Supporting Information ABSTRACT: The photochemistry of a model merocyaninespiropyran system was analyzed theoretically at the MS-CASPT2//SA-CASSCF(14,12) level. Several excited singlet states were studied in both the closed spiropyran and open merocyanine forms, and the paths to the different S1/S0 conical intersections found were analyzed. After absorption of UV light from the spiropyran form, there are two possible ultrafast routes to efficient conversion to the ground state; one involves the rupture of the Cspiro O bond leading to the open form and the other involves the lengthening of the CspiroN bond with no photoreaction. From the merocyanine side the excited state can reach a very broad S1/S0 conical intersection region that leads the system to the closed form after rotation of the central methine bond. Alternatively, rotation of the other methine bonds connects the system through different S1/S0 conical intersections to several merocyanine isomers. The present work provides a theoretical framework for the recent experimental results (Buback, J. J. Am. Chem. Soc. 2010, 132, 16101619) and sheds light on the complex photochemistry of these kinds of compounds.
’ INTRODUCTION Molecular photochromic switches1 have been broadly studied for their use in new technologies, including optical data storage, optical switching, and molecular logic gates.24 One of their main advantages is that they provide a method to control bulk properties by irradiation.5 One of the most studied molecular photochromic switch systems is the spiropyran molecule (SP) (10 -30 -dihydro-10 ,30 ,30 -trimethyl-spiro[2H-1-benzopyran20 ,20 -(2H)-indole).6 In this molecule the indole and benzopyran moieties are connected orthogonally at a spiro carbon atom (see Scheme 1). After absorption of a UV photon (λ
