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Abstract A great proportion of molecular crystals can be made to grow as twisted fibrils. Typically, this requires high crystallization driving forces that lead to spherulitic textures. Here, it is shown how micron size channels fabricated from poly(dimethylsiloxane) (PDMS) serve to collimate the circular polycrystalline growth fronts of optically banded spherulites of twisted crystals of three compounds, coumarin, 2,5‐bis(3‐dodecyl‐2‐thienyl)‐thiazolo[5,4‐d]thiazole, and tetrathiafulvalene. The relationships between helicoidal pitch, growth front coherence, and channel width are measured. As channels spill into open spaces, collimated crystals “diffract” via small angle branching. On the other hand, crystals grown together from separate channels whose bands are out of phase ultimately become a single in‐phase bundle of fibrils by a cooperative mechanism yet unknown. The isolation of a single twist sense in individual channels is described. We forecast that such chiral molecular crystalline channels may function as chiral optical wave guides.
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Tailor‐Made Auxiliaries for Polar Growth from Melts
Abstract Tailor‐made auxiliaries are generally less stereochemically discriminating of crystals grown from the melt than crystals grown from solution. However, it is possible to make supramolecular inferences using well‐chosen additives in the manner taught to us by Lahav and Leiserowitz. Spherulites manifesting needle‐like growth and small angle branching grow frequently from supercooled melts under high crystallization driving forces, along one principal crystallographic direction. If this direction is polar, it is important to establish its absolute sense as a basis for understanding growth at the interface between crystals and melt. This assignment, for polycrystalline ensembles, is beyond the capabilities of X‐ray crystallography. Two examples of this discrimination are described with tailor‐made additives, one for theβform of resorcinol and another for form I ofL‐malic acid. Assigning the absolute sense of a polar axis with molecular additives is a problem that resembles both the science and style of previous experiments from the Weizmann Institute.
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- Award ID(s):
- 1708716
- PAR ID:
- 10305112
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Israel Journal of Chemistry
- Volume:
- 61
- Issue:
- 9-10
- ISSN:
- 0021-2148
- Page Range / eLocation ID:
- p. 583-589
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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