title: New insights into the photoswitching mechanisms of normal dithienylethenes.
abstract: The photoswitching and competitive processes of the referent photochromic diarylethene derivative 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (DTE) and a novel bridged analog DTE-m5 have been investigated by state-of-the-art TD-DFT calculations and ultrafast spectroscopy supported by advanced chemometric data treatments. Focusing on DTE, the overall deactivation pathway of both antiparallel (AP) and parallel (P) conformers of the open form (OF) (1 : 1 in solution) has been resolved and rationalized starting from the Franck-Condon (FC) region to the ground state recovery. For the photo-excited P conformer, after ultrafast relaxation (∼200 fs) towards the S1relaxed state, an expected ISC occurred (55 ps) to produce a triplet state,3P, the latter relaxing within 2.5 μs. Concerning the AP conformer, the photocyclization reaction is reported to proceed immediately (100 fs) starting from the FC region while the relaxed singlet state is populated in parallel. For the first time, we discovered that the latter state evolves through an unexpected ISC process (1 ps) giving rise to a second triplet state,3AP. For DTE-m5, by slightly constraining the molecule with the bridge, this triplet becomes reactive and participates in the formation of 10% of closed form (CF) probably through an adiabatic mechanism. Concerning the photoreversion, in accordance with the literature, we report on a two-step process, a 190 fs vibrational relaxation followed by a 6 ps ring-opening reaction. For the overall species at the singlet or triplet manifold, the use of advanced MCR-ALS allows us to obtain specific spectral signatures. This study is therefore a new step within the comprehension of DTE photochemistry.
authors.affiliation: Univ. Lille, CNRS, UMR 8516, LASIR, Laboratoire de Spectrochimie Infrarouge et Raman, F59 000 Lille, France. stephane.aloise@univ-lille1.fr and Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA, Université de Tunis El Manar, 1060 Tunis, Tunisia.
authors.forename: I
authors.initials: I
authors.lastname: Hamdi
authors.affiliation: Univ. Lille, CNRS, UMR 8516, LASIR, Laboratoire de Spectrochimie Infrarouge et Raman, F59 000 Lille, France. stephane.aloise@univ-lille1.fr.
authors.forename: G
authors.initials: G
authors.lastname: Buntinx
authors.affiliation: Université Paris Diderot, Sorbonne Paris Cité, 5 rue Thomas Mann, 75205 Paris Cedex 13, France and Chimie Paris Tech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP), F-75005 Paris, France.
authors.forename: A
authors.initials: A
authors.lastname: Perrier
authors.affiliation: Univ. Lille, CNRS, UMR 8516, LASIR, Laboratoire de Spectrochimie Infrarouge et Raman, F59 000 Lille, France. stephane.aloise@univ-lille1.fr.
authors.forename: O
authors.initials: O
authors.lastname: Devos
authors.affiliation: Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA, Université de Tunis El Manar, 1060 Tunis, Tunisia.
authors.forename: N
authors.initials: N
authors.lastname: Jaïdane
authors.affiliation: Univ. Lille, CNRS, UMR 8516, LASIR, Laboratoire de Spectrochimie Infrarouge et Raman, F59 000 Lille, France. stephane.aloise@univ-lille1.fr.
authors.forename: S
authors.initials: S
authors.lastname: Delbaere
authors.affiliation: Univ. Lille, CNRS, UMR 8516, LASIR, Laboratoire de Spectrochimie Infrarouge et Raman, F59 000 Lille, France. stephane.aloise@univ-lille1.fr.
authors.forename: A K
authors.initials: AK
authors.lastname: Tiwari
authors.affiliation: Univ. Lille, CNRS, UMR 8516, LASIR, Laboratoire de Spectrochimie Infrarouge et Raman, F59 000 Lille, France. stephane.aloise@univ-lille1.fr.
authors.forename: J
authors.initials: J
authors.lastname: Dubois
authors.affiliation: Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo 1, Saga 840-8502, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Takeshita
authors.affiliation: Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo 1, Saga 840-8502, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Wada
authors.affiliation: Univ. Lille, CNRS, UMR 8516, LASIR, Laboratoire de Spectrochimie Infrarouge et Raman, F59 000 Lille, France. stephane.aloise@univ-lille1.fr.
authors.forename: S
authors.initials: S
authors.lastname: Aloïse