Highly luminescent diyne (-C C-CC-) containing hybrid polyphenyleneethynylene/poly(p-phenylenevinylene) polymer:: Synthesis and characterization

Luminophoric dialdehyde 1,4-bis[4-formylphenylethynyl-(2,5-dioctadecyloxyphenyl)-buta-1,3-diyne] (4) enables the synthesis of diyne-containing hybrid polyphenyleneethynylene/poly(p-phenylenevinylene) polymer poly [1,4-phenylene-ethynylene-1,4-(2,5-dioctadecyloxy)phenylene-butadi-1,3-ynylene-1,4-(2,5-dioctadecyloxy)phenylene-ethynylene-1,4-phenylene-ethene-1,2-diyl-1,4-(2,5-dioctadecyloxy)phenylene-ethene-1,2-diyl] (7) with a well-defined general structure (-Ph-CdropC-Ar-CdropC-CdropC-Ar-CdropC-Ph-CH=CH-Ar-CH=CH-)(n) which was confirmed by NMR and infrared spectroscopy. The highly luminescent material is thermostable, soluble in usual organic solvents through the grafting, of octadecyloxy side groups, and can be processed into transparent films. With the aim to investigate the effect of -CdropC-CdropC- in the photophysical behavior of 7, a comparison of the photophysics of monomers 3 [1,4-bis(4-formylphenylethynyl)-2,5-dioctadecyloxybenzene] and 4 and subsequently of their respective polymers 6 and 7 has been carried out. Similar photophysical behaviors for 6 (poly[1,4-phenylenethynylene -1,4-(2,5-dioctadecyloxyphenylene)ethene-1,2-diyl]) and 7 were observed in dilute CHCl3 solution as a result of an identical chromophore system responsible for the absorption (lambda(a) = 448 nm) and emission (lambda(f) = 490 nm) in both compounds. The increased planarization and enhanced rigidity of the conjugated backbone in the solid state at room temperature as well as in frozen dilute tetrahydrofuran solution at 77 K cause the bathochromic shift of the absorption and emission spectra. The large octadecyloxy side chains obviously limit strong pi-pi interchain interactions in the solid films, which explains the high fluorescence quantum yields of 35 and 52% obtained for 6 and 7, respectively. The energetically arduous migration of the 7 electron through the diyne units not only requires a higher threshold voltage for the detection of photoconductivity in 7 but could possibly limit radiationless deactivation channels of the exciton, which explains the approximate 20% fluorescence quantum yields difference between 6 and 7 in the solid state. The electron-withdrawing effect of the triple bonds confer both 6 and 7 with a good electron-accepting property (E-ox = 1.39 V vs Ag/AgCl) if used in light-emitting diode devices. (C) 2002 Wiley Periodicals, Inc.