One-dimensional photonic crystal (PC) with alternating layers of TiO(2) and SiO(2) was fabricated with spin coating and low temperature baking, resulting in a successful tuning of the PC stop band so as to block the amplified spontaneous emission (ASE) from a pi-conjugated polymer film. Single PC as a substrate, not a cavity with two PC's, of the polymer film was sufficient to shift the tangential ASE to the energy at PC stop band edge, indicating that the tangential ASE propagating along the interface was modulated by its evanescent-field tail in the PC, which opens a possibility for wide tuning of the coherent luminescence from an ultrathin pi-conjugated polymer film with ultimate mode volume.