In this study, five new phenylazo indoles derived from 1,2-dimethylindole were synthesized and characterized to evaluate the substituent effects on the molecular structures and absorption spectra. Theoretical calculations were carried out by density functional theory. The experimental and theoretical results are compared. X-ray single-crystal diffraction analyses reveal that the dyes have similar planar molecular conformation between azo and aromatic/heteroaromatic ring units but dissimilar crystal packing. The analysis of the electronic spectra showed that the electron-withdrawing groups (-Cl and -CN) were more effective than the electron-donating groups (-CH3 and -OCH3). Dyes containing electron-donating groups do not show significant changes relative to the parent dye, whereas the absorption maxima move to longer wavelengths for dyes containing electron-withdrawing groups. In addition, the absorption maxima exhibit the little bathochromic shifts for each dye with the increasing dielectric constants of the solvents. (C) 2013 Published by Elsevier Ltd.