Collimating the growth of twisted crystals of achiral compounds

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.

Self-Patterning Tetrathiafulvalene Crystalline Films

“…Looking forward, self-patterning organic electronic active layers present a low-cost strategy to form isolated semiconductor wires in order to reduce device crosstalk and leakage current that degrade device performance. Further control over wire placement could be achieved through the use of polymer molds to guide crystallization from the melt and collimate spherulitic bands . Because crystal twisting is expected to occur in at least one-third of all molecular compounds, the findings herein present a generalizable patterning method that does not require chemical synthesis.…”

Leveling up Organic Semiconductors with Crystal Twisting

“…Furthermore, the CR micrograph reveals that the spherulite is bisected into heterochiral semicircles, one dextrorotatory and the other levorotatory, corresponding to opposing twist senses. 127 We stress that the signal is not natural optical activity but arises in the sense of splay of thin anisotropic lamellae, as displayed in Figure 10b.…”

“…(a) Optical micrograph of BDT crystallized in the wavy channels of a PDMS mold between crossed polarizers and (b) corresponding map of the CR. Adapted with permission from ref . Copyright 2023, Wiley-VCH.…”

“…One promising strategy to overcome this limitation is to use polymer molds with prescribed geometries to spatially isolate bundles of homochiral twisted crystals. 127 Figure 11a displays BDT twisted crystals collimated in curved 100 μm wide, 5 μm tall channels in poly(dimethylsiloxane) (PDMS) molds between crossed polarizers. BDT was introduced into the channels in the melt phase through capillary forces and subsequently crystallized through rapid cooling below the melting point.…”

“…One promising strategy to overcome this limitation is to use polymer molds with prescribed geometries to spatially isolate bundles of homochiral twisted crystals Figure a displays BDT twisted crystals collimated in curved 100 μm wide, 5 μm tall channels in poly­(dimethylsiloxane) (PDMS) molds between crossed polarizers.…”