Synthesis, characterization, and fluorescence quenching of novel cationic phenyl-substituted poly(p-phenylenevinylene)s

Abstract

Three new phenyl-substituted poly(p-phenylenevinylene) (Ph-PPV) derivatives with amino-functionalized groups were synthesized through either Gilch reaction for poly{2,5-bis[4′-2-(N,N-diethylamino)ethoxyphenyl]-1,4-phenylenevinylene (P1) or Wittig reaction for poly{2,5-bis(4′-decyloxyphenyl)-1,4-phenylenevinylene-alt-2,5-bis[4′ -2-(N,N-diethylamino)ethoxyphenyl]-1,4-phenylenevinylene} (P2) and poly(2,5-bis{4′-2-[2-(2-methoxyethoxy)ethoxy]ethoxyphenyl}-1,4-phenylenevi nylene-alt-2,5-bis[4′-2-(N,N-diethylamino)ethoxyphenyl]-1,4- phenylenevinylene) (P3). Green light-emitting cationic polymers, poly{2,5-bis(4′-decyloxyphenyl)-1,4-phenylenevinylene-alt-2,5-bis[4′ -2-(N,N,N-triethylammonium)ethoxyphenyl]-1,4-phenylenevinylene} dibromide (P2′) and poly(2,5-bis{4′-2-[2-(2-methoxyethoxy)ethoxy]ethoxyphenyl}-1,4-phenylenevi nylene-alt-2,5-bis[4′-2-(N,N,N-triethylammonium)ethoxyphenyl]-1, 4-phenylenevinylene) dibromide (P3′), were prepared from the neutral polymers P2 and P3, respectively. Water solubility was achieved on P3′ through increase of the hydrophilicity of the side chains. The acid-assistant reversible solubility of P1 makes it promising in preparing light-emitting multilayer devices. On the basis of FT-IR and 1H NMR spectra, it was found that P1 is primarily of trans-vinyl while P2 and P3 are of 80% and 81% cis-vinyl, respectively, which depends on the polymerization method employed. The bulky phenyl substituents successfully impeded the interchain interaction which led to quantum efficiency as films comparable to that of solutions. Quaternization also resulted in more twisted conformation of the polymer main chain which was supported by both blue-shifted absorption and reduced quantum efficiency of P2′ and P3′ in solutions and as films than that of the neutral polymers. The fluorescence of P3′ was efficiently quenched by an anionic quencher Fe(CN)6 4-, Ksv of which is 3.3 × 106 M-1. However, a modified Stern-Volmer plot showed that 9% of the fluophores could not be accessible to the quencher, which may result from the twisted conformation or intermolecular aggregation.