We study the anchoring of 4-dimethyl-amino substituted azobenzene dyes doped liquid crystals and the formation of permanent gratings in the nematic liquid cristal 5CB. The increase on the dipolar interaction due to trans-cis isomerization, and the resulting anchoring to the substrate, is not enough to explain the formation of permanent gratings as it is commonly believed. We demonstrate that a strong interaction of the acid group in the 4-dimethylamino-2´-carboxylic acid substituted azo (Methyl Red, MR) dye can occur with the solid substrate through hydrogen bonding intermolecular interaction leading to permanent gratings in methyl red doped liquid crystal cells.