Dye-doped liquid-crystalline (LC) system is known to enhance its photoinduced reorientation behavior significantly compared to undoped LC system. However, aligned LC system is disturbed by thermal fluctuation at high irradiation intensity, due to excess thermal deactivation excited dye molecules with a low emission quantum yield. In this study, photoresponsive behavior of LC systems doped with photostable fluorescent π-conjugated molecules was investigated by irradiation with a single Ar+ laser beam. When the laser beam was incident on the sample cells, diffraction patterns were observed on a screen for the LC cell doped with coumarin derivatives. Appearance of the diffraction rings indicates photoinduced reorientation of LCs. Coumarin derivatives with long molecular length were found to act as efficient triggers for photoinduced reorientation of LCs.