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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 studyElectronic supplementary information (ESI) available. See DOI: 10.1039/c3pp25450j
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...
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| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Online Access: | Get full text |
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| Summary: | 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 L
a
ππ* mediated channel, the other involves an unprecedented weakly emissive state which plays a significant role in the overall deactivation processes. The L
a
ππ* channel features biphasic dynamics with time constants (
τ
1
/
τ
2
) 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
τ
1
of the L
a
ππ* population to the newly identified state followed by conversion in
τ
2
of the remaining L
a
ππ* molecules into the electronic ground state. The channel mediated by the weakly emissive species shows solvent-dependent dynamics with time constants (
τ
3
) 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 (
λ
max
∼ 520 nm) with polarization direction varied markedly from that of the L
a
ππ* but close to the L
b
ππ*. This species acts as an effective quenching state to the radiative decay of the brightly emissive L
a
ππ* and L
b
ππ*. It sets in promptly ( |
|---|---|
| ISSN: | 1474-905X 1474-9092 |
| DOI: | 10.1039/c3pp25450j |