6,13-pentacene diketone is a unique material which can be converted to pentacene only by photo irradiation. Drop-cast films of this soluble precursor of pentacene were prepared and their thin film properties were studied. The effect of solvent and photo irradiation conditions on photo-conversion behavior and film structures were investigated, compared to spin-cast films. The drop-cast films exhibited large plate-like crystals having a size of several microns, and showed intense peaks in X-ray diffraction. The electrical measurement using a field-effect transistor was also performed.