Low-temperature study of the molecular and crystal structures of 2-(2′-tosylamino-5′-nitrophenyl)-4H-3,1-benzoxazin-4-one, an organic luminophore

The crystal structure of 2-(2'-tosylamino-5'-nitrophenyl)-4H-3,1-benzoxazin-4-one (I) is studied by X-ray diffraction at 100 K (C21H15N3O6S, a = 20.899(2) Angstrom, b = 10.948(1) Angstrom, c = 8.260(1) Angstrom, V = 1889.3(1) Angstrom (3), Z = 4, and space group Pbn2(1)). The compound exhibits an anomalous Stokes shift. Upon cooling the oxazineaminophenyl fragment of compound I acquires a quinoid structure and the linear parameters of the intramolecular N-H . . .N hydrogen bond increase (the distance between the heterocyclic nitrogen atom and the hydrogen atom of the tosylamino group becomes 1.92 Angstrom). The complete optimization of the geometry of molecules in compound I and unsubstituted 2-(2'-tosylaminophenyl)-4H-3,1-benzoxazin-4-one in the ground singlet electronic state is performed by the semiempirical method with the MOPAC program. It is shown that the oxygen atoms in the sulfo group of molecule I are nonequivalent, because one of them is involved in the intermolecular C-H . . .O hydrogen bond. (C) 2001 MAIK "Nauka/Interperiodica".