[Problems] To provide a monomethine dye compound that enables formation of a thin film with high refractive index and excellent optical properties through formation of a homogeneous thin film of dye molecule J-association complex by easy means (spin coating technique) and that has high sensitivity and excels in short mark recording capability so as to be suitable for high speed recording and high density recording, and further to provide an optical information recording medium utilizing the monomethine dye compound and a process for producing the same.[Means for Solving Problems] Attention has been focused on employment of a spin coating technique so that a homogeneous thin film can be easily formed through coating; on using of a dye material capable of forming a J-association complex to thereby realize excellent optical properties (high refractive index); on using of an oxocyanine dye of high solubility as the dye material so as to enable employment of a solvent free from substrate erosion; on using of a dye exhibiting a large difference between refractive index before recording and refractive index after recording, the decomposition of the dye brought about by an endothermal reaction; etc. There is provided a monomethine dye compound of FIG. 1 characterized in that it is applicable onto a substrate by a spin coating technique.