The techniques of pulse radiolysis, laser flash photolysis and conventional flash photolysis have been used to study several properties of the lowest triplet states of a series of related carbonyl polyenes : ,!3-ionone, /3-ionylidene acetaldehyde, /3-apo-l4'-carotenal, P-ap0-8'-carotenal and torularhodinaldehyde. The corresponding triplet-triplet (T-T) absorption spectra, triplet lifetimes, triplet extinctions, quantum efficiencies of production of the lowest triplet for 265 nm excitation and lowest triplet energy levels have been estimated. Correlations between (i) the numbers of C=C double bonds (n) and the T-T wavelength maxima, (ii) the singlet-singlet and T-T wavelength maxima, (iii) the T-T maximum extinction coefficients and n and (iv) the lowest triplet energies and n, were found. The results obtained for the different carbonyl polyenes are discussed in terms of varying relative positions of (n, T*
The radical cations and anions of a number of carbonyl containing polyenes of biological importance have been generated, and their absorptions characterised using pulse radiolysis techniques. The wavelength maxima of the absorption bands are linearly dependent on the number of conjugated double bonds. The radical cation and the radical anion derived from the same parent molecule absorb at very similar wavelengths. There is a large hypsochromic shift in the radical anion absorption on changing from hexane to methanol solutions. The radical anions decay rapidly, in methanol, to form a species which is probably the protonated anion.
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