Photoisomerization dynamics of trans-trans, cis-trans, and cis-cis diphenylbutadiene from broadband transient absorption spectroscopy and calculations.

Krohn, O A; Quick, M; Sudarkova, S M; Ioffe, I N; Richter, C; Kovalenko, S A

Krohn, O A; Quick, M; Sudarkova, S M; Ioffe, I N; Richter, C; Kovalenko, S A.

Afiliación

Krohn OA; JILA and the Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.
Quick M; Department of Chemistry, Humboldt-Universität zu Berlin, Berlin, Germany.
Sudarkova SM; Department of Chemistry, Lomonosov Moscow State University, Moscow, Russia.
Ioffe IN; Department of Chemistry, Lomonosov Moscow State University, Moscow, Russia.
Richter C; Department of Chemistry, Humboldt-Universität zu Berlin, Berlin, Germany.
Kovalenko SA; Department of Chemistry, Humboldt-Universität zu Berlin, Berlin, Germany.

J Chem Phys ; 152(22): 224305, 2020 Jun 14.

Article en En | MEDLINE | ID: mdl-32534550

RESUMEN

The photoisomerization path and dynamics of trans-trans (ttD), cis-trans (ctD), and cis-cis (ccD) 1,4-diphenyl-1,3-butadiene (DPB) in solution are studied with broadband transient absorption (TA) spectroscopy and quantum chemical calculations. For ttD in n-hexane, 2-photon-excited TA spectra indicate that the 2Ag state is located above 1-photon allowed 1Bu (S1) by â¼1000 cm-1. Following S0 â S1 optical excitation, the isomerization occurs via torsion about a butadiene double bond to perpendicular molecular configuration P. The P-state is detected in ccD with an excited-state absorption band at 390 nm. This P-band develops during S1 â P half-torsion with time of 0.15 ps, followed further by P â S0 half-torsion and simultaneous decay with 1.6 ps in acetonitrile and 5 ps in n-hexane. In addition, two oscillation cycles between P and S1 population are observed before equilibration in n-hexane. For ctD, an indication of rising and decaying P is found in acetonitrile. The vast majority of ctD species photoisomerizes to ttD and not to ccD, in agreement a with calculated low torsional barrier about the cis double bond and high barrier about the trans double bond. Photoisomerization yield Y and time τi depend drastically on the solvent polarity. Thus, in n-hexane, the isomerization ttD â ctD has yield Ytt,ct = 0.1 and time τi = 829 ps, while in acetonitrile, Ytt,ct = 0.4 and τi = 27 ps. The 30-fold acceleration of the isomerization in acetonitrile clearly reflects a highly polar character of P, consistent with a dipole moment µP > 9.6 D. The results for DPB are discussed in comparison to stilbene.

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Texto completo: 1 Colección: 01-internacional Base de datos: MEDLINE Idioma: En Revista: J Chem Phys Año: 2020 Tipo del documento: Article País de afiliación: Estados Unidos Pais de publicación: Estados Unidos

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