title: Triplet energies and the singlet oxygen quenching mechanism for 7H-pyrazolo[5,1-c]-1,2,4-triazole azomethine dyes.
abstract: Analysis of triplet energy transfer rate constants gives the triplet energies of six 7H-pyrazolo[5,1-c]-1,2,4-triazole azomethine dyes, with lambda max values in the range 546-633 nm in ethanol, to lie in the range 115-88 kJ mol-1. Energy transfer rates from porphyrin and phthalocyanine sensitisers can be well approximated using the Balzani equation with a zero or small reorganization energy, and a transmission coefficient ca. 1/1000 that of the fully adiabatic value. A comparison of data on triplet energies of azomethine dyes suggests a relationship between the dye absorption energies and triplet energies of the form: ET = 0.69(+/- 0.04)(E lambda max)-33(+/- 9) kJ mol-1. A detailed study of the quenching of 1O2* by one of the dyes shows that this reaction is accompanied by isomerisation of the dye. This is interpreted as strong indirect evidence for an energy transfer mechanism for the process, a conclusion which is supported in a general way by the value of the 1O2* quenching rate constant.
authors.affiliation: Chemistry Department, University of Wales Swansea, Singleton Park, Swansea, UK SA2 8PP.
authors.forename: Peter
authors.initials: P
authors.lastname: Douglas
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Thomas
authors.forename: Holger
authors.initials: H
authors.lastname: Strohm
authors.forename: Chris
authors.initials: C
authors.lastname: Winscom
authors.forename: Dave
authors.initials: D
authors.lastname: Clarke
authors.forename: Michael S
authors.initials: MS
authors.lastname: Garley