Lifetime evidence for a weak lowest electronic transition in adenosine.
The fluorescence decay of adenosine in 1:1 glycol/water glass has been determined at 77K using narrow pulse (700 ps) laser excitation at 290 nm and fluorescence detection with a scanned narrow-gate (100 ps) fast sampler together with digital averaging. Data analysis by re-iterative non-linear least squares convolution shows the decay is best represented by the bi-exponential form I(t) = 0.59exp - t/1.2ns + 0.41 exp - t/7.0ns. This leads to intrinsic radiative lifetimes of 150 ns and 220 ns respectively and a combined oscillator strength of 1.5 x 10(-2). Compared with the overall oscillator strength of 0.29 for the entire first absorption band of adenosine this indicates that transitions to and from the lowest-lying state in this band are quite forbidden. This is not accounted for by current theoretical considerations.
Chemistry Department, Oregon State University, Corvallis 97331.
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Daniels
D000241:Adenosine; D005453:Fluorescence; D007834:Lasers; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014364:Tryptophan / Q000031:analogs & derivatives
C016952:N-acetyltryptophanamide; D014364:Tryptophan; D000241:Adenosine