Structural Volume Changes upon Photoisomerization: A Laser-Induced Optoacoustic Study with a Water-Soluble Nitrostilbene

  1. Michler, I. 3
  2. Feis, A. 23
  3. Rodríguez, M.A. 13
  4. Braslavsky, S.E. 3
  1. 1 Universidad de La Rioja
    info

    Universidad de La Rioja

    Logroño, España

    ROR https://ror.org/0553yr311

  2. 2 University of Florence
    info

    University of Florence

    Florencia, Italia

    ROR https://ror.org/04jr1s763

  3. 3 Max Planck Institute for Chemical Energy Conversion
    info

    Max Planck Institute for Chemical Energy Conversion

    Mülheim an der Ruhr, Alemania

    ROR https://ror.org/01y9arx16

Revista:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment & General Theory

ISSN: 1089-5639

Año de publicación: 2001

Volumen: 105

Número: 20

Páginas: 4814-4821

Tipo: Artículo

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DOI: 10.1021/JP004334M SCOPUS: 2-s2.0-0035942879 GOOGLE SCHOLAR

Otras publicaciones en: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment & General Theory

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Resumen

The trans to cis photoisomerization of 4,4′-dinitro-2,2′-disulfonylstilbene (DS) was studied by laser-induced optoacoustic spectroscopy (LIOAS) in aereated neat water and in aereated aqueous solutions of various monovalent cations (NH4+, N(CH3)4+, Na+, K+, and Cs+) and the respective cis to trans photoisomerization only in the presence of NH4+. In every case, two single-exponential components were required to fit the data, one with an unresolved lifetime (<20 ns) for the appearance of the triplet state mixture T (the perpendicular triplet state 3p* in equilibrium with the lowest trans triplet state 3t*) and one with a longer lifetime of (75 ± 20) ns at 5.5 °C for the decay of the T mixture. The temperature dependence of the LIOAS amplitudes in combination with the determined isomerization quantum yields afforded a contraction of -(1.4 ± 0.15) ml/mol for the trans to T transition, whereas a smaller contraction of -(0.15 ± 0.15) ml/mol was obtained for the cis to T transition. The different values of the contraction indicate a greater similarity between the average structures of the T components with the cis ground singlet state than with the trans ground singlet. The total structural volume change for the trans to cis transition is in average ΔVtc = - (1.2 ± 0.1) ml/mol. The calculated contribution of electrostriction is at most 50% of this value. However, the nature of the countercation had no influence on the data as would be expected for changes in the specific interaction with the H-bond network in water upon photoisomerization. Thus, ca. 50% of the total contraction is attributed to intrinsic effects, related to a shorter C=C bond and a smaller accessible volume in the cis isomer. The LIOAS data show that cis-DS lies (28 ± 35) kJ/mol above trans-DS in agreement with the calculated value of 37 kJ/mol.