| Autor: |
Trachsel, Maria A., Blaser, Susan, Siffert, Luca, Wiedmer, Timo, Leutwyler, Samuel |
| Předmět: |
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| Zdroj: |
Journal of Chemical Physics; 9/28/2019, Vol. 151 Issue 12, pN.PAG-N.PAG, 15p, 4 Diagrams, 6 Charts, 9 Graphs |
| Abstrakt: |
The S1 excited-state lifetime of jet-cooled 1-ethylcytosine (1ECyt) is ∼1 ns, one of the longest lifetimes for cytosine derivatives to date. Here, we analyze its S0 → S1 vibronic spectrum using two-color resonant two-photon ionization and UV/UV holeburning spectroscopy. Compared to cytosine and 1-methylcytosine, the S0 → S1 spectrum of 1ECyt shows a progression in the out-of-plane "butterfly" mode ν 1 ′ , identified by spin-component scaled-second-order coupled-cluster method ab initio calculations. We also report time-resolved S1 state nonradiative dynamics at ∼20 ps resolution by the pump/delayed ionization technique. The S1 lifetime increases with the number of ν 1 ′ quanta from τ = 930 ps at v 1 ′ = 0 to 1030 ps at v 1 ′ = 2 , decreasing to 14 ps at 710 cm−1 vibrational energy. We measured the rate constants for S1 ⇝ S0 internal conversion and S1 ⇝ T1 intersystem crossing (ISC): At the v′ = 0 level, kIC is 8 × 108 s−1 or three times smaller than 1-methylcytosine. The ISC rate constant from v′ = 0 to the T1(3ππ*) state is kISC = 2.4 × 108 s−1, 10 times smaller than the ISC rate constants of cytosine, but similar to that of 1-methylcytosine. Based on the calculated S1(1ππ*) state radiative lifetime τrad = 12 ns, the fluorescence quantum yield of 1ECyt is Φfl ∼ 7% and the intersystem crossing yield is ΦISC ∼ 20%. We measured the adiabatic ionization energy of 1-ethylcytosine via excitation of the S1 state as 8.353 ± 0.008 eV, which is 0.38 eV lower than that of amino-keto cytosine. Measurement of the ionization energy of the long-lived T1(ππ*) state formed via ISC reveals that it lies 3.2–3.4 eV above the S0 ground state. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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