Fluorescence emission from the first- and the second-excited π-singlet states of aromatic hydrocarbons in solution, and their temperature dependences
- 1 January 1974
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
- Vol. 70, 267-273
- https://doi.org/10.1039/f29747000267
Abstract
Earlier studies on the temperature dependence of the fluorescence emission from dilute deoxygenated n-heptane solutions of aromatic hydrocarbons have been extended from 1,12-benzperylene and 3,4-benzpyrene to 1,2-benzanthracene, 2′-methyl-1,2-benzanthracene, 3,4-benzotetraphene, and 3-methylpyrene. For these molecules, the energy separation, Es2.0–Es1.0, between the first, S1, and the second, S2, excited π-singlet states lies in the range 1200 to 2500 cm–1. In all cases, fluorescence emission from S2 to the ground state S0,n has been clearly observed. For each molecule studied, the ratio of the integrated fluorescence quantum intensity from S2 to that from S1 increases with increasing temperature and, for the molecules investigated, it decreases with increasing Es2,0–Es1.0. Our present and earlier experimental results indicate that: (i) the S2 fluorescence is primarily a result of thermal repopulation of S2 from a lower level, (ii) the S2 fluorescence is quite intense (especially at elevated temperatures) for aromatic molecules which have close lying first- and second-excited π-singlet states, (iii) the internal conversion process between S2 and S1 cannot be regarded as being completely irreversible, and (iv) the fluorescence emission from the second excited π-singlet state of aromatic molecules in solution is not uncommon.Keywords
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