No abstract

Well-defi ned conjugated oligomers ( Sn ) containing from 1 to 8 units of a tricyclic building block involving a dioctyloxybenzothiadiazole unit with two thienyl side rings ( S1 ) are synthesized by a bottom-up approach. UV-Vis absorption data of solutions show that chain extension produces a narrowing of the HOMO-LUMO gap (Δ E ) to values slightly smaller than that of the parent polymer ( P1 ). Plots of Δ E and of the band gap of fi lms ( E g ) versus the reciprocal chain length show that Δ E and E g converge towards a limit corresponding to an effective conjugation length (ECL) of 7-8 S1 units. UV-Vis absorption and photoluminescence data of solutions and solid fi lms show that chain extension enhances the propensity to inter-chain aggregation. This conclusion is confi rmed by GIXD analyses which reveal that the edge-on orientation of short-chain systems evolves toward a face-on orientation as chain length increases while the π-stacking distance decreases beyond 7 units. The results obtained on solution-processed BHJ solar cells show a progressive improvement of power conversion effi ciency (PCE) with chain extension; however, the convergence limit of PCE remains inferior to that obtained with the polymer. These results are discussed with regard to the role of mono/ polydispersity and chain aggregation.

Supramolecular light-emitting polymers (SLEPs) based on host-guest interactions were developed for solution processed organic electronic devices. The dibenzo-24-crown-8 functionalized blue-emitting conjugated oligomer 1 and green-emitting conjugated oligomer 3 were used as the host materials, and the dibenzylammonium salt functionalized blue-emitting conjugated oligomer 2 was used as the guest material. The resulting linear SLEPs were obtained from the self-organization of the host and guest oligomers, which were confirmed by the nuclear magnetic resonance, viscosity and differential scanning calorimetry studies. Highly fluorescent SLEP nanofibers can be easily obtained by drawing or electronspinning from the equimolar solution of the host and guest oligomers. The photophysical and electroluminescence properties of the resulting SLEPs were fully investigated. It was found that the SLEPs' emission colors can be well tuned from blue to green with significantly enhanced photoluminescent efficiencies by using 3 as the dopant, which is due to the efficient energy transfer caused by the exciton trapping on narrow band gap host oligomer 3 in the SLEPs. As a result, the designed SLEPs showed comparable electroluminescence device performances to those analogous traditional conjugated polymers. Considering the precisely defined starting monomers and catalyst-free polymerization process for the designed SLEPs, combining the good device performances, the present study provides a promising alternative route to develop solution processed semiconductors for optoelectronic applications.

Blending morphology evolves with polymer chain propagation with reduced phase separation scale and increased phase purity while blending morphological stability is dominated by the miscibility between the donor and acceptor.