STRUCTURE AND FLUORESCENT PROPERTIES OF LUMINESCENT DYES DERIVED FROM 7-DIMETHYLAMINO-1, 4-BENZOXAZIN-2-ONE

The molecular structure of four luminescent dyes derived from 7-dimethylamino-1, 4-benzoxazin-2-one have been determined by molecular mechanics. The crystal structure of one of them, namely, 7-dimethylamino-3-benzyl-1, 4-benzoxazin-2-one was also determined by single crystal X-ray diffractometry. Of the two rings in the fused ring system, the heterocycle assumes a distorted chair conformation while the other, a distorted half-chair conformation, both exhibiting very small derivations from planarity in all the compounds. Optical characterization of these dyes and dyes derived from xanthene showed that the Stokes shift values of these dyes are higher while the fluorescence quantum yields are lower than those of the latter. These have been explained on the basis of the dipole moments and molecular sizes and on the structural mobility of the molecular fragments.