Preparation and Absorption Spectral Properties of the Nitrogen Analogs of a Pechmann Dye and Its Isomeric Pyrano[4,3-c]pyran-1,5-dione

Abstract

Bathochromic shifts were observed by replacement of the ladoneoxygen atoms in a Pechmm dye with nitrogen atoms, while hypsochromic shifts were caused by replacement of the lactone-oxygen atoms in a pyrano[4,3-clpyran-1,Sdione with nitrogen atoms. It is well known that coplanarity of two aromatic rings in biphenyls is hindered by o,o-and o',o'-substituents.A blue pigment, trichotomine dimethyl ester (la) has a planar structure."In a previous paper, we reported the preparation and spectroscopic properties of 1,l'-diacyltrichotomine derivatives (lb), in which loss of coplanarity between the 1,l'-diacyl carbonyl groups and the trichotomine chromophore was indicated by the absorption and 13C NMR spectra.Ib The C, C' rings in l a seem to keep coplanarity of the indole rings and the central bis-pyrrolone plane, and cleavage of the C(5) -C(6) and C(5') -C(6') bonds in l a seems to cause twist ofthe indole rings relative to the central plane.We planed to study the spectroscopic properties of twisted chromophores.It is reported that a Pecbmm dye (2) gives a colored