Abstract
The short-lived T1 state of 1,4-diphenylbutadiyne (DPB) has been investigated in various glassy matrices at low temperatures using time-resolved EPR and pulsed EPR methods. Zero-field splitting parameters of D = −0.250 cm-1 and E = +0.018 cm-1 were determined. The negative D value was verified from the MS dependence of the ENDOR frequencies. The hyperfine splitting constants of ring protons were obtained from the electron spin−echo envelope modulation with three-pulse stimulated echo. The spin density distribution on the phenyl groups was estimated from the analysis of the hyperfine splittings at each of the canonical orientations. The moderate spin densities on the phenyl rings indicated that the T1 state was 3πxπx* in electronic character. The origin of the large negative D value of DPB has been discussed in terms of the spin−orbit interaction between the close lying 3πxπx* and 3πxπy* states.
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