Large Dynamic Stokes Shift of DNA Intercalation Dye Thiazole Orange has Contribution from a High-Frequency Mode
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- 作者：Venugopal Karunakaran ; J. Luis Pé ; rez Lustres ; Lijuan Zhao ; Nikolaus P. Ernsting ; and Oliver Seitz
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：March 8, 2006
- 年：2006
- 卷：128
- 期：9
- 页码：2954 - 2962
- 全文大小：551K
- 年卷期：v.128,no.9(March 8, 2006)
- ISSN：1520-5126
文摘
Fluorescence of the cyanine dye Thiazole Orange (TO) is quenched by intramolecular twistingin the excited state. In polypeptide nucleic acids, a vibrational progression in a 1400 cm-1 mode dependson base pairing, from which follows that the high-frequency displacement is coupled to the twist coordinate.The coupling is intrinsic to TO. This is shown by femtosecond fluorescence upconversion and transientabsorption spectroscopy with the dye in methanol solution. Narrow emission from the Franck-Condonstate shifts to the red and broadens within 100 fs. The radiative rate does not decrease during this process.Vibrational structure builds up on a 200 fs time scale; it is assigned to asymmetric stretching activity in themethine bridge. Further Stokes shift and decay are observed over 2 ps. Emission from the global S1 minimumis discovered in an extremely wide band around 12 000 cm-1. As the structure twists away from the Franck-Condon region, the mode becomes more displaced and overlap with increasingly higher vibrational wavefunctions of the electronic ground state is achieved. Twisting motion is thus leveraged into a fast-shrinkingeffective energy gap between the two electronic states, and internal conversion ensues.