Combinatorial synthesis and screening for blue luminescent π-conjugated polymer thin film

Two series of random copolymers (poly(PP-ran-MP)s which consist of p-phenylene, PP, and m-phenylene, MP, units and poly(PPy-ran-MPy)s which consist of p-pyridine, PPy, and m-pyridine, MPy, units) with various monomeric unit ratios were prepared. Thin films of poly(PP-ran-MP)s were combinatorially deposited by vacuum evaporation with a fixed mask and slit masks on a quartz glass, and poly(PPy-ran-MPy)s were superposed on the poly(PP-ran-MP)s layer. The thin film of poly(PP-ran-MP) containing the PP and MP units in a 5:5 ratio, poly(PP-ran-MP-5/5), showed 7.6 times stronger blue photoluminescence (PL), compared with the thin films of poly(p-phenylene), PPP, and poly(m-phenylene), PMP, homopolymers. The PL intensity of the film of poly(PP-ran-MP-5/5) was much stronger than the sum of the PL intensities of the films of PPP and PMP. Furthermore, [poly(m-pyridine), PMPy/poly(PP-ran-MP-5/5)] bi-layer film emitted blue light of about 3 times stronger intensity than the poly(PP-ran-MP-5/5) monolayer film. An alternating copolymer of p-phenylene and m-phenylene, poly(PP-alt-MP-5/5) was prepared by a Stille coupling reaction and its PL peak was observed at about 50 nm shorter wavelength than that of poly(PP-ran-MP-5/5).