Control of electronic states of dye molecules (organic semiconductors) by introducing appropriate substituent groups has been examined. NH2 (electron-releasing group) and NO2 (electron-withdrawing group) were introduced in thiacarbocyanine dye to modify the electronic states of the dyes. The effect of modification was examined based on the properties of photoelectric cells made by the dye derivatives. Clear increase in photocurrent, more than ten times, was observed when modified dyes were used instead of the original dye. The result shows that the introduction of substituent groups for organic semiconductors is quite effective to control the electronic states, and the introduction can be regarded as doping in molecular level.