A series of new mesogenic azobenzene propanediols with nitro, methoxy, cyano and no substituent have been synthesized and their mesomorphic behavior mapped. The diols are employed in a melt transesterification with di-Ph tetradecanedioate to produce side-chain polyesters with high molar masses. Diols and polyesters have similar UV-visible spectra reflecting the acceptor character of the substituent. Polarization FTIR spectroscopy has been used to det. the mesogenic order parameter for the polyesters with different substituents at four laser irradn. wavelengths (413, 458, 488 and 515 nm). Diffraction gratings in thin polyester films have been recorded through polarization holog. Cyano and unsubstituted azobenzene polyesters are shown to exhibit the highest diffraction efficiencies on the order of 13%.