title: Photoisomerization of disperse red 1 studied with transient absorption spectroscopy and quantum chemical calculations.
abstract: The photoisomerization of the push-pull substituted azo dye Disperse Red 1 is studied using femtosecond time-resolved absorption spectroscopy and other spectroscopic and computational techniques. In comparison with azobenzene, the pipi* state is more stabilized by the effects of push-pull substitution than the npi* state, but the latter is probably still the lowest in energy. This conclusion is based on the kinetics, anisotropy of the excited state absorption spectrum, the spectra of the ground states, and quantum chemical calculations. The S(1)(npi*) state is formed from the initially excited pipi* state in <0.2 ps, and decays to the ground state with time constants of 0.9 ps in toluene, 0.5 ps in acetonitrile, and 1.4 ps in ethylene glycol. Thermal isomerization transforms the Z isomer produced to the more stable E isomer with time constants of 29 s (toluene), 28 ms (acetonitrile), and 2.7 ms (ethylene glycol). The pathway of photoisomerization is likely to be rotation about the N=N bond. Quantum chemical calculations indicate that along the inversion pathway ground and excited state energy surfaces remain well separated, whereas rotation leads to a region where conical intersections can occur. For the ground-state Z to E isomerization, conclusive evidence is lacking, but inversion is more probably the favored pathway in the push-pull substituted systems than in the parent azobenzene.
authors.affiliation: Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands.
authors.forename: Mirosława
authors.initials: M
authors.lastname: Poprawa-Smoluch
authors.forename: Jacob
authors.initials: J
authors.lastname: Baggerman
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.forename: Huub P A
authors.initials: HP
authors.lastname: Maas
authors.forename: Luisa
authors.initials: L
authors.lastname: De Cola
authors.forename: Albert M
authors.initials: AM
authors.lastname: Brouwer
mesh_terms: D001391:Azo Compounds / Q000737:chemistry* / Q000528:radiation effects*; D008956:Models, Chemical; D015394:Molecular Structure; D010777:Photochemistry; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D014466:Ultraviolet Rays
chemical_list: D001391:Azo Compounds; C069318:Disperse Red 1