Photochromic formazans: Raman spectra, X-ray crystal structures, and 13C magnetic resonance spectra of the orange and red isomers of 3-ethyl-1,5-diphenylformazan
Abstract
The X-ray crystal structures of the two isomers of a photochromic formazan have been determined. Red 3-ethyl-1,5-diphenylformazan belongs to the orthorhombic space group P212121 and adopts a syn,s-trans-configuration. The orange, light-stable isomer, belongs to the monoclinic space group P21/c and adopts an anti,s-trans-configuration. Raman and 13C n.m.r. spectra for the orange isomer both in the solid state and in solution confirm that the solution species retains the structure established for the solid state. The Raman spectrum for the red isomer in the solid state shows the shifts to lower wavenumber for the azo group stretching vibration characteristics of the syn,s-trans-configuration.