Odd−Even Effects and the Influence of Length and Specific Positioning of Alkoxy Side Chains on the Optical Properties of PPE−PPV Polymers

Abstract

This contribution reports the combined influences of odd-eVen effects and the specific positioning of alkoxy side chains OR 1 ) (OC n+10 H 2(n+10)+1 ) and OR 2 ) (OC n H 2n+1 ) (with n ) 6, 7, 8, 9) on the phenylene-ethynylene and phenylene-Vinylene segments, respectively, on the optical properties of hybrid polymers P(n+10)/n of general repeating unit: -Ph-CtC-Ph-CtC-Ph-CHdCH-Ph-CHdCH-. For the polymeric materials, visual color impression varies alternatively between orange red (P16/6 and P18/8) and yellow (P17/7 and P19/9) according to the odd and eVen features of the alkoxy side chains, where odd or eVen relates to the total number of sp 3 -hybridized atoms within the side chains. This side chain related effect is ascribed to both absorptive and emissive behaviors of the polymers on the basis of photophysical investigations in the bulk. Almost identical thin film absorption spectra were obtained for all four materials; however, the photoluminescence of the odd polymers, P16/6 (λ f ) 556 nm) and P18/8 (λ f ) 614 nm), was red-shifted relative to that of their eVen counterparts (λ f ) 535 nm). Further, the P18/8 maximum at 614 nm can be readily assigned to excimer emission, as evidenced by the largest Stokes shift (5600 cm -1 ), largest fwhm f -value (3700 cm -1 ), and the lowest Φ f -value of 24%. The strong π-π interchain interaction in P18/8, due to loose alkoxy side chains packing, does not only favor fluorescence quenching but also enable an effective inter-as well as intra-molecular recombination of the generated positive and negative polarons in electroluminescence, which explains the good EL properties of this polymer irrespective of the solvent used. A voltage-dependent blue shift of the EL spectra of up to 100 nm was observed for P18/8 devices prepared from aromatic solvents. This red to green EL shift as observed with increasing voltage is assigned to conformational changes of the polymer chains with increasing temperature.

p‐Phenyleneethynylene Molecular Wires: Influence of Structure on Photoinduced Electron‐Transfer Properties

“…Further reaction of 8 with p-ethynylbenzaldehyde (6) led to 9 together with the homocoupling product 10 in low yields. [24] Although different experimental conditions were tested to improve the yield, the best results were obtained by employing tetrakis(triphenylphosphane)-palladium as the catalyst and diisopropylamine as the base at reflux in toluene (Tol). Under these conditions, the desired compound 9 was obtained in a yield of 65 % (Table 1).…”

Odd−Even Effect in Free Radical Polymerization of Optically Active 2,5-Bis[(4‘-alkoxycarbonyl)- phenyl]styrene

“…16 A similar phenomenon has also been observed in chiral polythiophene, 17 polysilylene aggregates, 18 and optically active polyfluorenes and poly-p-phenylenevinylene in solid films. 19,20 Masuda reported a conflicting system. 21,22 In five helical poly(propiolic ester)s with chiral moieties that possessed identical stereogenic centers, but different numbers of methylene groups between the ester group and asymmetric atom, only one showed weak positive optical rotation ([R] D ) +4°) and all the other four displayed strong negative optical rotations ([R] D ) -340°-612°).…”

CuI as versatile hole-selective contact for organic solar cell based on anthracene-containing PPE–PPV

“…The variety of conjugated polymer-fullerene systems used as the active layers leads to very individual demands on the holecontact side, which cannot be covered by PEDOT:PSS alone [20][21][22]. This argument applies in particular for the non-thiophenebased polymers that use p-phenylene-ethynylene and p-phenylene-vinylene (PPE-PPV) backbones as an example [23][24][25][26][27]. Here the interface matching with PEDOT:PSS can suffer from detrimental energy level offsets and/or degradation effects attributed to residual water, ionic species and the layer's acidity [28,10].…”

“…Specifically, we use high molecular weight anthracene-containing poly (p-phenylene-ethynylene)-alt-poly (p-phenylene-vinylene) (PPE-PPV) with and without statistical distribution of octyloxy and 2-ethylhexyloxy side chains as active layers in combination with PCBM (see Fig. 1a) [23][24][25][26][27]. CuI as an interfacing layer is sandwiched between the active matrix and the final contact on the anode-side.…”