title: Fast photodynamics of azobenzene probed by scanning excited-state potential energy surfaces using slow spectroscopy.
abstract: Azobenzene, a versatile and polymorphic molecule, has been extensively and successfully used for photoswitching applications. The debate over its photoisomerization mechanism leveraged on the computational scrutiny with ever-increasing levels of theory. However, the most resolved absorption spectrum for the transition to S1(nπ*) has not followed the computational advances and is more than half a century old. Here, using jet-cooled molecular beam and multiphoton ionization techniques we report the first high-resolution spectra of S1(nπ*) and S2(ππ*). The photophysical characterization reveals directly the structural changes upon excitation and the timescales of dynamical processes. For S1(nπ*), we find that changes in the hybridization of the nitrogen atoms are the driving force that triggers isomerization. In combination with quantum chemical calculations we conclude that photoisomerization occurs along an inversion-assisted torsional pathway with a barrier of ~2 kcal mol(-1). This methodology can be extended to photoresponsive molecular systems so far deemed non-accessible to high-resolution spectroscopy.
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Eric M M
authors.initials: EM
authors.lastname: Tan
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Saeed
authors.initials: S
authors.lastname: Amirjalayer
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Szymon
authors.initials: S
authors.lastname: Smolarek
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Alexander
authors.initials: A
authors.lastname: Vdovin
authors.affiliation: Dipartimento di Chimica 'G. Ciamician', Università di Bologna, via F. Selmi 2, I-40126 Bologna, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Zerbetto
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Wybren Jan
authors.initials: WJ
authors.lastname: Buma