Dipole Moments of the Excited States of Azulene

Abstract

The splitting of spectral lines by an electric field, in the accepted sense, is dependent on the interaction of the field with degenerate states. However, molecular crystals having no degenerate molecular states can be subject to a linear Stark mixing due to the interaction of the field with the inequivalent molecules in the unit cell. In a dilute mixed crystal where the guest–guest interactions are vanishingly small, the resultant splitting of spectral lines, $\mathrm{\Delta S\hspace{0.17em}=\hspace{0.17em}EG\Delta \mu }$ , is directly proportional to the field strength $E$ , a geometrical factor $G$ , and the change in dipole moment $\mathrm{\Delta \mu }$ between the ground and excited states. The substitutional solid of azulene in naphthalene was chosen to demonstrate this effect. The dipole moments of the first and second singlet states of azulene have geen determined and are −0.42 and −0.31 D, respectively.