title: Multistate photo-induced relaxation and photoisomerization ability of fumaramide threads: a computational and experimental study.
abstract: Fumaric and maleic amides are the photoactive units of an important and widely investigated class of photocontrollable rotaxanes as they trigger ring shuttling via a cis-trans photoisomerization. Here, ultrafast decay and photoinduced isomerization in isolated fumaramide and solvated nitrogen-substituted fumaramides (that are employed as threads in those rotaxanes) have been investigated by means of CASPT2//CASSCF computational and time-resolved spectroscopic techniques, respectively. A complex multistate network of competitive deactivation channels, involving both internal conversion and intersystem crossing (ISC) processes, has been detected and characterized that accounts for the picosecond decay and photochemical/photophysical properties observed in the singlet as well as triplet (photosensitized) photochemistry of fumaramides threads. Interestingly, singlet photochemistry appears to follow a non-Kasha rule model, where nonequilibrium dynamical factors control the outcome of the photochemical process: accessible high energy portions of extended crossing seams turn out to drive the deactivation process and ground-state recovery. Concurrently, extended singlet/triplet degenerate regions of twisted molecular structures with significant spin-orbit-coupling values account for ultrafast (picosecond time scale) ISC processes that lead to higher photoisomerization efficiencies. This model discloses the principles behind the intrinsic photochemical reactivity of fumaramide and its control.
authors.affiliation: Dipartimento di Chimica "G.Ciamician", Universita di Bologna, via Selmi 2, 40126 Bologna, Italy.
authors.forename: Piero
authors.initials: P
authors.lastname: Altoè
authors.forename: Natalia
authors.initials: N
authors.lastname: Haraszkiewicz
authors.forename: Francesco G
authors.initials: FG
authors.lastname: Gatti
authors.forename: Piet G
authors.initials: PG
authors.lastname: Wiering
authors.forename: Céline
authors.initials: C
authors.lastname: Frochot
authors.forename: Albert M
authors.initials: AM
authors.lastname: Brouwer
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Balkowski
authors.forename: Daniel
authors.initials: D
authors.lastname: Shaw
authors.forename: Sander
authors.initials: S
authors.lastname: Woutersen
authors.forename: Wybren Jan
authors.initials: WJ
authors.lastname: Buma
authors.forename: Francesco
authors.initials: F
authors.lastname: Zerbetto
authors.forename: Giorgio
authors.initials: G
authors.lastname: Orlandi
authors.forename: David A
authors.initials: DA
authors.lastname: Leigh
authors.forename: Marco
authors.initials: M
authors.lastname: Garavelli