Entropic changes control the charge separation process in triads mimicking photosynthetic charge separation

Alberto C. Rizzi, Maurice Van Gastel, Paul A. Liddell, Rodrigo E. Palacios, Gary F. Moore, Gerdenis Kodis, Ana L Moore, Thomas A Moore, John Devens Gust, Silvia E. Braslavsky

Research output: Contribution to journalArticle

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Abstract

Laser-induced optoacoustic spectroscopy (LIOAS) measurements with carotene-porphyrin-acceptor "supermolecular" triads (C-P-A, with A = C60, a naphthoquinone NQ, and a naphthoquinone derivative, Q) were carried out with the purpose of analyzing the thermodynamic parameters for the formation and decay of the respective long-lived charge separated state C ̇+-P-A-. The novel procedure of inclusion of the benzonitrile solutions of the triads in Triton X-100 micelle nanoreactors suspended in water permitted the separation of the enthalpic and structural volume change contributions to the LIOAS signals, by performing the measurements in the range 4-20 °C Contractions of 4.2, 5.7, and 4.2 mL mol-1 are concomitant with the formation of C·+-P-A ·- for A = C60, Q and NQ, respectively. These contractions are mostly attributed to solvent movements and possible conformational changes upon photoinduced electron transfer, due to the attraction of the oppositely charged ends, as a consequence of the giant dipole moment developed in these compounds upon charge separation (∼110 D). The estimations combining the calculated free energies and the LIOAS-derived enthalpy changes indicate that entropy changes, attributed to solvent movements, control the process of electron transfer for the three triads, especially for C-P-C60 and C-P-Q. The heat released during the decay of 1 mol of charge separated state (CS) is much smaller than the respective enthalpy content obtained from the LIOAS measurements for the CS formation. This is attributed to the production of long-lived energy storing species upon CS decay.

Original languageEnglish
Pages (from-to)4215-4223
Number of pages9
JournalJournal of Physical Chemistry A
Volume112
Issue number18
DOIs
Publication statusPublished - May 8 2008

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Photoacoustic spectroscopy
polarization (charge separation)
Naphthoquinones
Lasers
spectroscopy
contraction
lasers
Enthalpy
electron transfer
decay
enthalpy
Nanoreactors
carotene
Electrons
Porphyrins
Dipole moment
Octoxynol
Micelles
Carotenoids
porphyrins

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Rizzi, A. C., Van Gastel, M., Liddell, P. A., Palacios, R. E., Moore, G. F., Kodis, G., ... Braslavsky, S. E. (2008). Entropic changes control the charge separation process in triads mimicking photosynthetic charge separation. Journal of Physical Chemistry A, 112(18), 4215-4223. https://doi.org/10.1021/jp712008b

Entropic changes control the charge separation process in triads mimicking photosynthetic charge separation. / Rizzi, Alberto C.; Van Gastel, Maurice; Liddell, Paul A.; Palacios, Rodrigo E.; Moore, Gary F.; Kodis, Gerdenis; Moore, Ana L; Moore, Thomas A; Gust, John Devens; Braslavsky, Silvia E.

In: Journal of Physical Chemistry A, Vol. 112, No. 18, 08.05.2008, p. 4215-4223.

Research output: Contribution to journalArticle

Rizzi, Alberto C. ; Van Gastel, Maurice ; Liddell, Paul A. ; Palacios, Rodrigo E. ; Moore, Gary F. ; Kodis, Gerdenis ; Moore, Ana L ; Moore, Thomas A ; Gust, John Devens ; Braslavsky, Silvia E. / Entropic changes control the charge separation process in triads mimicking photosynthetic charge separation. In: Journal of Physical Chemistry A. 2008 ; Vol. 112, No. 18. pp. 4215-4223.
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