Triplet excited states of carbonyl-containing polyenes

Abstract

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: β-ionone, β-ionylidene acetaldehyde, β-apo-14′-carotenal, β-apo-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 CC 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, π*) and (π, π^*) levels in the corresponding singlet and triplet manifolds.