Polythiophenes with Thiophene Side Chain Extensions: Convergent Syntheses and Investigation of Mesoscopic Order

Buffer Chain Model for Understanding Crystallization Competition in Conjugated Polymers

It remains challenging to comprehensively understand the packing models of conjugated polymers, in which side chains play extremely critical roles. The side chains are typically flexible and non-conductive and are widely used to improve the polymer solubility in organic solutions. Herein, a buffer chain model is proposed to describe link between conjugated backbone and side chains for understanding the relationship of crystallization competition of conductive conjugated backbones and non-conductive side chains. A longer buffer chain is beneficial for alleviating such crystallization competition and further promoting the spontaneous packing of conjugated backbones, resulting in enhanced charge transport properties. Our results provide a novel concept for designing conjugated polymers towards ordered organization and enhanced electronic properties and highlight the importance of balancing the competitive interactions between different parts of conjugated polymers.

Controlling the organization and stretchability of poly(3-butylthiophene) spherulites

In this work, we report a simple strategy to readily prepare poly(3-butylthiophene) (P3BT) films with patterned spherulites by brushing the P3BT film surface and annealing the film with carbon disulfide (CS₂) vapor. The spherulites nucleated preferentially at the mechanically scratched areas over the unscratched region of the film. The ridge (formed at the side of the scratch) hinders the diffusion of the P3BT molecules, promoting the aggregation and nucleation of P3BT along the ridge to form spherulites upon the CS₂ vapor-annealing. The sizes of the ridge and the scratch have no effect on the nucleation and crystallization of the patterned spherulites. We evaluated the crack formation of the P3BT films with patterned spherulites in response to mechanical stretching along different directions. When the stretching direction was parallel to the scratching direction, cracks appeared preferentially at the boundary between the ordered spherulites. In contrast, cracks occurred first at the boundary of stochastic nucleated spherulites located away from the patterned spherulites, when the stretching direction was perpendicular to the scratching direction. The patterned spherulites with regulated mechanical properties may find applications in the design and fabrication of stretchable organic optoelectronic devices with enhanced stability and durability.

Push-pull thiophene chromophores for electro-optic applications: from 1D linear to β-branched structures

We report the synthesis and characterization of a novel series of push-pull chromophores bearing 1D linear and β-branched thiophenes as π-conjugated spacers between a 2,2,4,7-tetramethyl-1,2,3,4-tetrahydroquinoline electron donor unit and dicyano- and tricyanovinylene electron acceptor groups. The effect of the introduction of β-thiophenes on the linear and nonlinear (NLO) optical properties as well as electrochemical and thermal data is studied in detail by performing a comparative study between the branched and 1D linear systems. In addition, a parallel DFT computational study is used to evaluate structure-property relationships. The non-linear optical behavior of the molecules both in solution and in solid state as electro-optic (EO) films using a guest-host approach shows very promising performance for electro-optic applications with high molecular first hyperpolarizabilities (μβ) of 4840 × 10^-48 esu and electro-optic coefficients r₃₃ reaching 650 pm V^-1. One highlight is that the electro-optic films of the β-branched chromophores are superior in terms of thermal stability in device operation as measured by a transmissive modified reflective Teng-Man method. This work provides guidelines for the design of improved electro-optic materials including β-branched chromophores which could be useful for practical EO applications, where both enhanced β and r₃₃ values together with chemical and thermal stability are necessary.