We developed a novel coupler, hydroxyperinone, 2- and/or 5-hydroxy-7H-benz[de]benzimidazo[2,1-a]isoquinoline-7-one and synthesized a bisazo pigment from the novel coupler. The OPC using this bisaszo pigments showed better characteristics in sensitivity and cyclic stability than the OPC using bisazo pigments derived from Naphthol AS. ¹³C NMR spectra of these bisazo pigments indicated that the dominant tautomer of the new bisazo pigment in the solid state was different from those of other bisazo pigments. The difference in tautomers reflects their characteristics. We designed and synthesized a unique highly sensitive unsymmetrical bisazo pigment having a large dipole moment in the excited state, on the basis of the photocarrier generation process model. Thermally stimulated current measurements were applied to elucidate factors for high sensitivity.