Publications by authors named "St John Whittaker"
A previously unreported polymorph of 5,11-bis(triisopropylsilylethynyl)anthradithiophene (TIPS ADT), Form II, crystallizes from melt-processed TIPS ADT films blended with 16 ± 1 wt % medium density polyethylene (PE). TIPS ADT/PE blends that initially are crystallized from the melt produce twisted TIPS ADT crystals of a metastable polymorph (Form IV, space group 1̅) with a brickwork packing motif distinct from the slipstack packing by solution-processed TIPS ADT crystals (Form I, space group 2/) at room temperature. When these films were cooled to room temperature and subsequently annealed at 100 °C, near a PE melting temperature of 110 °C, Form II crystals nucleated and grew while consuming Form IV.
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- The performance of crystalline organic semiconductors is significantly influenced by their solid-state structure, particularly how the conjugated components are oriented in relation to device platforms.
- Engineering crystal orientation through chromophore modification is challenging, as traditional processing techniques provide limited control over this aspect.
- Crystal twisting has emerged as a novel method that enhances the properties of organic semiconductors, enabling the introduction of chiral characteristics and improving performance in applications like chiral sensing and optical telecommunications.
Tetrathiafulvalene (TTF) crystals grown from the melt are organized as spherulites in which helicoidal fibrils growing radially from the nucleation center twist in concert with one another. Alternating bright and dark concentric bands are apparent when films are viewed between crossed polarizers, indicating an alternating pattern of crystallographic faces exposed at the film surface. Band-dependent reorganization of the TTF crystals was observed during exposure to methanol vapor.
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- Many molecular crystals can grow as twisted fibrils, typically requiring strong crystallization forces that create specific textures.
- Micron-sized channels made from PDMS help direct the growth of these twisted crystals, leading to unique structural formations.
- The research highlights how these channels can influence the shape and coherence of the crystals, suggesting potential applications in chiral optical technologies.
Many molecular crystals (approximately one third) grow as twisted, helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance, charge-transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. Here, the effect of twisting on charge mobility is better analyzed for a monocomponent organic semiconductor, 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole (BDT), that forms twisted crystals with varied helicoidal pitches and makes possible a correlation of twist strength with carrier mobility.
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