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Investigation of the S1/ICT-->S0 internal conversion lifetime of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al: dependence on conjugation length and solvent polarity.
J Phys Chem A. 2007 Mar 29; 111(12):2257-65.JP

Abstract

The ultrafast internal conversion (IC) dynamics of aldehyde-substituted apocarotenoids (n'-apo-beta-caroten-n'-als with n=4, 8 and 12) have been investigated in a systematic variation of conjugation length and solvent polarity using time-resolved femtosecond transient absorption spectroscopy. After excitation to the S2 state with different excess energies, the subsequent intramolecular dynamics were investigated at several probe wavelengths covering the S0-->S2 and S1/ICT-->Sn absorption bands. Time constants tau1 for the internal conversion process S1/ICT-->S0 of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al have been newly measured. We compared these results with our earlier measurements for 12'-apo-beta-caroten-12'-al (D.A. Wild, K. Winkler, S. Stalke, K. Oum, T. Lenzer Phys. Chem. Chem. Phys. 2006, 8, 2499). In the case of the aldehyde with the longest conjugation (4'-apo-beta-caroten-4'-al), tau1 is almost independent of solvent polarity (4-5 ps), whereas a significant reduction of tau1 from 22.7 to 8.6 ps for the shorter 8'-apo-beta-caroten-8'-al and an even more pronounced reduction from 220 to 8.0 ps for 12'-apo-beta-caroten-12'-al were observed when the solvent medium was changed from n-hexane to methanol, respectively. In n-hexane, tau1 of the apocarotenals is strongly dependent on the conjugation length and this can be well understood in terms of an energy gap law description where the S1-S0 energy differences were estimated from their steady-state fluorescence spectra. In highly polar solvents, the IC to S0 is very fast, irrespective of the conjugation length. This is probably due to the stabilization of an intramolecular charge transfer (ICT) state in 12'-apo-beta-caroten-12'-al and 8'-apo-beta-caroten-8'-al. In the case of 4'-apo-beta-caroten-4'-al, such an influence of an ICT state is presumably less important than for the other two apocarotenals.

Authors+Show Affiliations

Max-Planck-Institut für biophysikalische Chemie, Abt. Spektroskopie und Photochemische Kinetik (10100), Am Fassberg 11, D-37077 Göttingen, Germany.No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

17388322

Citation

Ehlers, Florian, et al. "Investigation of the S1/ICT-->S0 Internal Conversion Lifetime of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al: Dependence On Conjugation Length and Solvent Polarity." The Journal of Physical Chemistry. A, vol. 111, no. 12, 2007, pp. 2257-65.
Ehlers F, Wild DA, Lenzer T, et al. Investigation of the S1/ICT-->S0 internal conversion lifetime of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al: dependence on conjugation length and solvent polarity. J Phys Chem A. 2007;111(12):2257-65.
Ehlers, F., Wild, D. A., Lenzer, T., & Oum, K. (2007). Investigation of the S1/ICT-->S0 internal conversion lifetime of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al: dependence on conjugation length and solvent polarity. The Journal of Physical Chemistry. A, 111(12), 2257-65.
Ehlers F, et al. Investigation of the S1/ICT-->S0 Internal Conversion Lifetime of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al: Dependence On Conjugation Length and Solvent Polarity. J Phys Chem A. 2007 Mar 29;111(12):2257-65. PubMed PMID: 17388322.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Investigation of the S1/ICT-->S0 internal conversion lifetime of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al: dependence on conjugation length and solvent polarity. AU - Ehlers,Florian, AU - Wild,Duncan A, AU - Lenzer,Thomas, AU - Oum,Kawon, Y1 - 2007/03/07/ PY - 2007/3/29/pubmed PY - 2007/7/28/medline PY - 2007/3/29/entrez SP - 2257 EP - 65 JF - The journal of physical chemistry. A JO - J Phys Chem A VL - 111 IS - 12 N2 - The ultrafast internal conversion (IC) dynamics of aldehyde-substituted apocarotenoids (n'-apo-beta-caroten-n'-als with n=4, 8 and 12) have been investigated in a systematic variation of conjugation length and solvent polarity using time-resolved femtosecond transient absorption spectroscopy. After excitation to the S2 state with different excess energies, the subsequent intramolecular dynamics were investigated at several probe wavelengths covering the S0-->S2 and S1/ICT-->Sn absorption bands. Time constants tau1 for the internal conversion process S1/ICT-->S0 of 4'-apo-beta-caroten-4'-al and 8'-apo-beta-caroten-8'-al have been newly measured. We compared these results with our earlier measurements for 12'-apo-beta-caroten-12'-al (D.A. Wild, K. Winkler, S. Stalke, K. Oum, T. Lenzer Phys. Chem. Chem. Phys. 2006, 8, 2499). In the case of the aldehyde with the longest conjugation (4'-apo-beta-caroten-4'-al), tau1 is almost independent of solvent polarity (4-5 ps), whereas a significant reduction of tau1 from 22.7 to 8.6 ps for the shorter 8'-apo-beta-caroten-8'-al and an even more pronounced reduction from 220 to 8.0 ps for 12'-apo-beta-caroten-12'-al were observed when the solvent medium was changed from n-hexane to methanol, respectively. In n-hexane, tau1 of the apocarotenals is strongly dependent on the conjugation length and this can be well understood in terms of an energy gap law description where the S1-S0 energy differences were estimated from their steady-state fluorescence spectra. In highly polar solvents, the IC to S0 is very fast, irrespective of the conjugation length. This is probably due to the stabilization of an intramolecular charge transfer (ICT) state in 12'-apo-beta-caroten-12'-al and 8'-apo-beta-caroten-8'-al. In the case of 4'-apo-beta-caroten-4'-al, such an influence of an ICT state is presumably less important than for the other two apocarotenals. SN - 1089-5639 UR - https://www.unboundmedicine.com/medline/citation/17388322/Investigation_of_the_S1/ICT__>S0_internal_conversion_lifetime_of_4'_apo_beta_caroten_4'_al_and_8'_apo_beta_caroten_8'_al:_dependence_on_conjugation_length_and_solvent_polarity_ L2 - https://dx.doi.org/10.1021/jp0676888 DB - PRIME DP - Unbound Medicine ER -