The solvent effect and identification of a weakly emissive state in nonradiative dynamics of guanine nucleosides and nucleotides--a combined femtosecond broadband time-resolved fluorescence and transient absorption study
| Autor: | Chopen Chan Wut Cheng, Keith Yat Fung Ho, Wai Ming Kwok, Chensheng Ma, Chris Tsz Leung Chan |
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| Rok vydání: | 2013 |
| Předmět: |
education.field_of_study
Quenching (fluorescence) Guanine Methanol Population Deoxyguanine Nucleotides Deoxyguanosine Water Photochemistry Fluorescence Photoexcitation chemistry.chemical_compound Spectrometry Fluorescence chemistry Excited state Ultrafast laser spectroscopy Solvents Physical and Theoretical Chemistry Solvent effects Ground state education |
| Zdroj: | Photochemicalphotobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology. 12(8) |
| ISSN: | 1474-9092 |
| Popis: | A combined method of femtosecond broadband time-resolved fluorescence (fs-TRF) and transient absorption (fs-TA) was employed to investigate the excited state dynamics of 2′-deoxyguanosine (dG) and 2′-deoxyguanosine 5′-monophosphate (dGMP). Comparative fs-TRF and fs-TA measurements were conducted on dG and dGMP in neutral water, deuterated water, and methanol with excitation wavelengths of 245, 267 and 285 nm. Very similar results were observed with dG and dGMP. The data provide compelling evidence for the co-existence of two nonradiative pathways. One is the generally recognized Laππ* mediated channel, the other involves an unprecedented weakly emissive state which plays a significant role in the overall deactivation processes. The Laππ* channel features biphasic dynamics with time constants (τ1/τ2) of ∼0.2/0.8 ps in water and ∼0.25/1.0 ps in methanol. The biphasic decay arises due to a partial transfer with τ1 of the Laππ* population to the newly identified state followed by conversion in τ2 of the remaining Laππ* molecules into the electronic ground state. The channel mediated by the weakly emissive species shows solvent-dependent dynamics with time constants (τ3) of ∼2.0 ps in water, ∼2.3 ps in deuterated water, and ∼4.1 ps in methanol. The species features absorption at UV wavelengths (∼300–400 nm) and exhibits deeply red-shifted fluorescence (λmax ∼ 520 nm) with polarization direction varied markedly from that of the Laππ* but close to the Lbππ*. This species acts as an effective quenching state to the radiative decay of the brightly emissive Laππ* and Lbππ*. It sets in promptly ( |
| Databáze: | OpenAIRE |
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