On the Role of Single Regiodefects and Polydispersity in Regioregular Poly(3-hexylthiophene): Defect Distribution, Synthesis of Defect-Free Chains, and a Simple Model for the Determination of Crystallinity

Abstract

Identifying structure formation in semicrystalline conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between physical properties, structure formation, and device parameters of regioregular, semicrystalline poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and molecular weight. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl(2) as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group analysis and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different molecular weights is synthesized via new, soluble nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering experiments, allow the development of a simple model for estimating the degree of crystallinity. We find very good agreement for predicted and experimentally determined degrees of crystallinities as high as ∼70%. For Ni(dppp)Cl(2)-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter determining crystallinity within the molecular weight range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicrystalline conjugated polymers as well.

Defect-free Naphthalene Diimide Bithiophene Copolymers with Controlled Molar Mass and High Performance via Direct Arylation Polycondensation

“…For semicrystalline polymers dispersity is known to influence the degree of crystallinity. 35 Additionally, fractionated crystallization can occur which complicates the extraction of melting enthalpies for low-molar-mass materials. 36 However, the dispersities for both DAP and Stille controls were very similar (see Table SI -2), and a correlation with melting enthalpies does not seem to be the case.…”

Energy transfer in pendant perylene diimide copolymers

“…While previous research has focused on utilising the π-π interactions of perylene monomers for supramolecular assembles that display exciton transport, [30][31][32][33] the use of polymers as a spatial scaffold with controlled inter-chromophore spacing for organising dye molecules is one potential method of allowing higher PDI concentrations without aggregation. Incorporating a low concentration emitter species enables FRET and minimises reabsorption losses.…”

Controlled synthesis of poly(3-hexylthiophene) in continuous flow

“…The tolyl–nickel species 3 is soluble and shows good stability in THF in an inert environment. Further, polymers initiated with this complex showed lower defect levels [23–24]. After successfully experimenting with this catalyst in batch conditions, the reagent was applied in flow processing for the synthesis of P3HT (Scheme 1).…”