Photolyses of tetraphenylcyclobutanes at 254 nm.
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概要
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Photolyses of 1,2,3,4-tetraphenylcyclobutanes (TPCB) at 254 nm in hydrocarbon solvents have been studied by means of fluorometry, nanosecond time-resolved spectroscopy, and measurements of the reaction quantum yields. The photolysis of TPCB originates from the S<SUB>1</SUB>(π,π<SUP>*</SUP>) state to give <I>trans</I>-stilbene nearly concertedly at higher temperatures (>200 K). Significant temperature and cis-effects were observed. The radiationless rate constants for the dissociation (<I>k</I><SUB>r</SUB>) and the other radiationless (<I>k</I><SUB>n</SUB>) processes decreased with lowering temperature. The value of <I>k</I><SUB>r</SUB> for γ-1,<I>t</I>-2,<I>t</I>-3,<I>c</I>-4-TPCB at 300 K, for example, was 4.7 times greater than that for γ-1,<I>t</I>-2,<I>c</I>-3,<I>t</I>-4-TPCB. The Arrhenius parameters of the relaxation processes were also determined. No intramolecular excimer emission was observed.
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