title: Rationalization and Design of Enhanced Photoinduced Cycloreversion in Photochromic Dimethyldihydropyrenes by Theoretical Calculations.
abstract: This study presents a computational investigation of the initial step of the dimethyldihydropyrene (DHP) to cyclophanediene (CPD) photoinduced ring-opening reaction using time-dependent density functional theory (TD-DFT). In particular, the photochemical path corresponding to the formation of the CPD precursor (CPD*) on the zwitterionic state is scrutinized. The TD-DFT approach was first validated on the parent compound against accurate ab initio calculations. It confirms that CPD* formation is efficiently quenched in this system by an easily accessible S2/S1 conical intersection located in the vicinity of the CPD* minimum and leading to a locally excited state minimum responsible for DHP luminescence. Increased ring-opening quantum yields were observed in benzo[e]-fused-DHP (DHP-1), isobutenyl-DHP (DHP-2), and naphthoyl-DHP (DHP-3). The calculations show that CPD* formation is much more favorable in these systems, either due to an inversion of electronic states in DHP-1, suppressing the formation of the locally excited state, or due to efficient stabilization of CPD* on the S1 potential energy surface in DHP-2 and DHP-3. Both effects can be combined in a rationally designed benzo[e]-fused-naphthoyl-DHP (DHP-4) for which we anticipate an unprecedented efficiency.
authors.affiliation: †Laboratoire de Chimie et Physique Quantiques (UMR5626), CNRS et Université de Toulouse 3, Toulouse, France.
authors.forename: Martial
authors.initials: M
authors.lastname: Boggio-Pasqua
authors.affiliation: ‡Laboratoire de Chimie (UMR5182), École Normale Supérieure de Lyon/CNRS et Université de Lyon 1, Lyon, France.|§Dipartimento di Chimica "G. Ciamician", Universita' degli Studi di Bologna, Via Selmi 2, I-40126 Bologna, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Garavelli