Efficient photoexcitation energy transfer in extended TT-electron conjugated molecules is a key factor in applications of such systems as a gain media in signal-amplifying fluorescent chemodetectors. Here we report an unprecedented ratiometric fluorescence amplification phenomenon in the surface-immobilized monolayers of oligo(p-phenylene ethynylene)s end-capped with a lower energy gap receptor group. The process of covalent immobilization on the surface results in monolayer films with improved molecular organization, which display highly efficient excitation energy transfer to the tower energy receptor groups. Chemical transformation of a subtle fraction of the receptor groups on the surface leads to a very significant fluorescent ratiometric response. While fundamental understanding of this unusual "turn-on" amplification phenomenon requires further studies, it can be used to develop thin-film ratiometric fluorescent chemosensors with improved optical gain.