Synthesis and Luminescent Studies of Poly(phenylenevinylene)s Containing a Biphenyl Moiety

Abstract

The polymers discussed in this contribution consist of phenylenevinylene chromophores linked together across flexible biphenyl “hinges” to shorten the effective conjugation length and to give sufficiently twisted structures that interchain aggregation is limited or prevented. They are poly[(2,5-dihexyloxy-p-phenylenevinylene)-alt-(4,4‘-dihexyloxy-3,3‘-biphenylenevinylene)] (1), poly[(2,5-dihexyloxy-p-phenylenevinylene)-alt-(2,2‘-dihexyloxy-3,3‘-biphenylenevinylene)] (2), and poly[(2,5-dihexyloxy-p-phenylenevinylene)-alt-(2,2‘-biphenylenevinylene)] (3). Absorption spectra in dilute solution and solid states are very similar for 1−3, consistent with the absence of aggregation effects in their ground electronic states. Photoluminescence emission spectra showed substantial red shifts in the solid state relative to dilute solution phase spectra. Solution emission quantum yields ranged from 0.26 to 0.42. LEDs based on 1−3 gave blue-green emission with maxima in the 480−510 nm range. The similarity of the photoluminescence and electroluminescence spectra for the polymers is consistent with emission from the same or very similar excited-state species. For LEDs based upon the highest quantum efficiency photoluminescent emitter, 1, better luminance was achieved using PEDOT-PSS hole injection layers in double-layer LEDs than using PPV.

One‐ and Two‐Photon Photochemistry and Photophysics of Poly(arylenevinylene)s Containing a Biphenyl Moiety

“…The oligomers 1 – 3 were synthesized by condensation between the corresponding bisaldehydes and bisphosphonates according to the literature procedure of Sarker et al20 Their elemental and spectral properties were consistent with the literature results. Matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) spectrometry and gel‐permeation chromatography (GPC) showed the degrees of polymerization/oligomerization to range from about 3–11 units.…”

“…The substitution pattern of these substances was chosen to encourage nonplanar ground‐state geometries20 as a result of repulsion between vinylic hydrogen atoms and the ortho CH of the adjacent phenyl ring, combined with the hinge effect of the biaryl units. Therefore, the effective conjugation length should be short in 1 – 3 .…”

“…TPA of the corresponding monomer should be small if this model is justified. The monomer is, according to the synthetic approach used for synthesis of 1 – 3 ,20 not available. The question furthermore concerns the structure of model monomers.…”

“…In particular, the determination of the effective conjugation length disclosed by the use of the Strickler–Berg relationship19 provides new insights regarding the quantification of photonic properties. Synthetic and preliminary photophysical work for 1 – 3 has been described elsewhere 20…”

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“…PPV has many good characteristics such as good charge carrier mobility, formation of high molecular weight polymers, soluble in common solvents, processability, and highly luminescence intensity which make PPV more attractive than many other conjugated systems 22. Bulky‐PPVs were reported using cycloalkoxyl,23–25 adamantyl,26, 27 cholestanyl,28, 29 aryloxy,30–33 and inorganic pendants like silyl34 and silsesquioxane35, 36 in the conjugated backbone. However, most of the successful bulky‐PPVs were found insoluble or partially soluble in common solvents, which hampered their processability, complete structural‐characterization, and so forth 26, 28.…”