Triplet energies, singlet state properties and singlet oxygen quenching rate constants and quantum yields for two cyan azamethine dyes

The triplet energies of two photographic cyan azamethine dyes with absorption maxima around 640 nm have been studied using time-resolved energy transfer methods and found to be 94 (+/-4) and 87 (+/-4) kJ mol(-1). The rate constants for the quenching of singlet molecular oxygen by the two dyes in ethanol are 6.5 (+/-0.5) x 10(9) and 6.7 (+/-0.5) x 10(9) mol(-1) dm(3) s(-1), close to the diffusion-controlled limit. Quantum yields of singlet oxygen production in air-equilibrated ethanol are 3.3 (+/-1.0) x 10(-5) and less than or equal to 1 x 10(-5). Fluorescence spectra of the dyes in dibutyl phthalate at relatively high concentration have been obtained leading to estimates of 6.9 (+/-1.2) x 10(-5) and 1.8 (+/-0.5) x 10(-5) for the quantum yields of fluorescence. Excited singlet state radiative and non-radiative rate constants, calculated using the Strickler Berg method, for the two dyes are: 9.9 (+/-0.4) x 10(7) and 1.5 (+/-0.2) x 10(12) s(-1); 8.7 (+/-0.7) x 10(7) and 5.0 (+/-2.0) x 10(12) s(-1). (C) 1999 Elsevier Science S.A. All rights reserved.