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Issue 37, 2016
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Triplet state formation and quenching dynamics of 2-mercaptobenzothiazole in solution

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Abstract

The photochemical dynamics of the thione 2-mercaptobenzothiazole (MBT) initiated by absorption of 330 nm ultraviolet light are investigated by ultrafast transient absorption spectroscopy. The lowest energy triplet state (T1) has mixed 3ππ*/3nπ* character and is populated with a quantum yield of 0.58 ± 0.01 from the photo-excited 1ππ* S2 state in methanol solution via rapid internal conversion to the 1nπ* S1 state (with time constant τ1 < 150 fs). The spectroscopic evidence points to a mechanism involving intersystem crossing from S1 to the 3nπ*/3ππ* T2 state (τ2 = 400 ± 100 fs) and internal conversion to T1 (with time constant for growth τ3 = 6.1 ± 0.4 ps). The remainder of the photoexcited molecules return to the ground state by S1 → S0 internal conversion. In methanol solution, the T1 state is long-lived but when the solvent is changed to styrene, triplet quenching is observed with a time constant of 107 ± 8 ps and assigned to the adduct-mediated energy transfer process MBT (T1) + styrene (S0) → 3[MBT–styrene] → MBT (S0) + Styrene (T1). Transient vibrational absorption spectroscopy observes the 3[MBT–styrene] biradical intermediate and determines its lifetime to be 700 ± 80 ps. Computational studies identify the mechanistic pathway for triplet quenching, which involves a curve crossing between two triplet states of the MBT–styrene adduct. The quenching process occurs with high efficiency, and no long-lived isomers of the initial adduct are observed.

Graphical abstract: Triplet state formation and quenching dynamics of 2-mercaptobenzothiazole in solution

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Publication details

The article was received on 22 Jul 2016, accepted on 07 Sep 2016 and first published on 07 Sep 2016


Article type: Paper
DOI: 10.1039/C6CP05110C
Citation: Phys. Chem. Chem. Phys., 2016,18, 26224-26235
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    Triplet state formation and quenching dynamics of 2-mercaptobenzothiazole in solution

    D. Koyama and A. J. Orr-Ewing, Phys. Chem. Chem. Phys., 2016, 18, 26224
    DOI: 10.1039/C6CP05110C

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