Supramolecular mechanofluorophores based on charge-transfer (CT) interactions between fluorescent pyrene and naphthalene diimide(s) with a tandem structure are newly developed and incorporated into the mid-chain of poly(ε-caprolactone)s. The fluorescence (FL) is quenched by the intramolecular CT interactions even at low concentrations both in solution and in the polymer matrix, and turn-on FL is induced upon application of mechanical forces.