The fluorescence and tautomerism of adenine

Abstract

AbstractWhen adenine is dissolved in alcohols at reduced temperatures the quantum yield of its fluorescence increases rapidly with decreasing wavenumber of excitation. This is attributed to competitive UV‐absorption of tautomers having different fluorescence yields. From studies on the fluorescence of alkyl‐derivatives of adenine, the author concludes that the tautomers are (N7‐H)‐adenine and (N9‐H)‐adenine:magnified imageThe concentrations and fluorescence yields of the proposed tautomers and their absorption spectra have been derived from the measured fluorescence action spectrum, the mirror image of the fluorescence spectrum, and the total UV‐absorption. The concentrations, 6% (N7‐H)‐adenine and 94% (N9‐H)‐adenine, are relatively insensitive to the type of alcohol and temperature. The fluorescence quantum yield of the (N9‐H)‐tautomer is low (Φ(9) ⩽ 0.002), and the yield of the (N7‐H)‐tautomer is high (Φ(7) = 0.2 in isobutanol at 170 °K) and sensitive to the type of alcohol and temperature. The solvent‐induced radiation‐less conversion of the (N7‐H)‐adenine depends on the cohesion and rigidity of the solvent, and is faster than Debye rotation.