Fluorescence Photoswitching in Polymer Matrix: Mutual Influence between Photochromic and Fluorescent Molecules by Energy Transfer Processes

The fluorescence photoswitching of photochrome-fluorophore (PF) mixtures based on 1,2-bis(5′-ethoxy-2′-(2”-pyridyl) thiazolyl) perfluorocyclopentene (P) and pyrromethene 597 (F) were studied. Polymethylmethracrylate (PMMA) films were fabricated with respective concentrations of 1.0 × 10−2 mol L−1 for P, and 9.2 × 10−4 and 9.2 × 10−3 mol L−1 for F. By alternate UV (λOF = 334 nm) and visible (λCF = 547 nm) irradiations, inducing the reaction between the opened (P-OF) and closed (P-CF) forms of P, both fluorescence intensity and lifetime can be reversibly modified and visualized in the micrometer scale by fluorescence imaging. Switching (writing/erasing) and reading functions are respectively borne by P and F. The interaction between the two units owes to an energy transfer based quenching of fluorescence, which operates in the P-CF state but not P-OF. The reading process alters only very weakly the state of P. During the writing process, the presence of F accelerates the P-CF to P-OF reaction, as evidenced by following the absorption spectrum change. The efficiency of the energy transfer was determined by Gösele’s model for the two concentrations of F and for concentrations of P-CF from 0 to 1.0 × 10−2 mol L−1. This model fits well with the experimental fluorescence intensity change during the photoreaction and can account for the origin of the above-mentioned acceleration. In addition, we demonstrated that switching one molecule of P-OF to P-CF could quench up to eight molecules of F. This “amplification” of the fluorescence signal was modeled as a function of the concentrations of both species, providing a tool to optimize the PF system composition.