The Excited States of Acridine Dyes. I. An ESR Study of the Triplet State

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Abstract
The lowest triplet state of acridine dyes has been studied by an ESR technique over a wide range of concentration and in various solvents. The ESR spectra of the triplet state have been observed at a resonance field of ca. 1550 gauss, corresponding to the ΔM=2 transitions. The ESR data characteristic of the triplet state depend on the dye concentration; this has been interpreted as being due to the association of dye molecules. The values of the zero-field splitting parameter, D*, calculated from the ΔM=2 transition spectra lead to the assignment of the lowest triplet state of acridine dyes as the (π−π*) state.