Enabling Control over Mechanical Conformity and Luminescence in Molecular Crystals: Interaction Engineering in Action

Abstract

Molecular crystals of p-conjugated molecules are of great interest as the highly orderedd ense packing offers superior chargea nd excitont ransport compared with its amorphous counterparts. However,i ntegration into optoelectronic devices remains am ajor challenge owing to its inherently brittlen ature. Herein, controlo ver the mechanical conformity in single crystals of pyridine-appended thiazolothiazole derivatives is reported by modulating the molecular packingt hrough interaction engineering. Twop olymorphs were prepared by achieving control over the thermodynamic/kinetic factors of crystallization;o ne of the polymorphs exhibits elasticb ending whereas the other is brittle.T he controlo ver the bending ability wasa chieved by forming co-crystals with hydrogen/halogen bond donors. As eamless extended crisscross pattern with respectt ot he bend plane through ad itopic hydrogen-bonding motif showedt he highest compliance towards mechanicalb ending, whereas the co-crystals with al ayered crisscross arrangementw ith segregated layers of co-formers exhibit slightly lower bending conformity.T hese results update the rationaleb ehind the plastic/elastic bending in molecular crystals. The co-crystals of ditopic halogen bond co-assemblies are particularly appealing for waveguidinga pplications as the co-crystals blend high mechanical flexibility and luminescence properties. The hydrogen bonded co-crystals are non-emissive in natureo wing to excited state protont ransfer dynamics. The rationalebehind the fluorescencep roperties of thesem aterials was also established from DFT calculations in aq uantum mechanics/molecular mechanics (QM/MM) framework.

Structural Study of Hydrogen-Bond Driven Cocrystallization of Pyridyl-Bithiophene Based Compounds

“…32−34 Recently, hydrogen-bond interactions have been gaining attention in electronic materials due to their efficient charge transport properties. 35,36 There are a limited number of studies where a systematic investigation has been conducted to understand how to manipulate and control the solid-state structure of a target compound.…”

“…Hydrogen-bonds, due to their directionality and strength, − are the most extensively used noncovalent interaction in crystal engineering. Although hydrogen-bonds have been investigated for over a century, it is still difficult to predict and control the intermolecular interaction in molecular packing. − Recently, hydrogen-bond interactions have been gaining attention in electronic materials due to their efficient charge transport properties. , There are a limited number of studies where a systematic investigation has been conducted to understand how to manipulate and control the solid-state structure of a target compound.…”

“…T1 and T2 are structural isomers due to the presence of 3-pyridine and 4-pyridine moieties. These target compounds were selected for the following reasons,: (a) thiophene compounds are known to have good electronic properties, and (b) pyridine is a good hydrogen-bond acceptor . The coformers used in this study are carboxylic acids, which act as very good hydrogen-bond donors.…”

Photomechanical crystalline materials: new developments, property tuning and applications

“…Polymorphs of a molecule have different molecular conformations, stacking or interaction patterns. 124,125 Polymorphism is a means of regulating material functions such as morphology, 126 mechanical properties, 127 and photoreactive properties of materials, 128 which are closely related to photomechanical behaviors. But polymorphs are not easy to obtain in general, so successful cases in this field are precious.…”

Recent Developments in Polymeric Assemblies and Functional Materials by Halogen Bonding

“…Further, this group showed polymorphism in crystal structures of a pyridyl‐functionalized thiazolothiazole derivative ( PyTTZ ) that exhibited blue and green emission in its flexible B‐form and brittle G‐form, respectively (Figure 18B) [89] . The effectiveness of X‐bonding and H‐bonding in gaining control over the bending flexibility of the polymorph‐B were examined through co‐crystallization with 1,4‐diiodotetrafluorobenzene ( DITFB ), tetrafluorohydroquinone ( TFHQ ), pentafluorophenol ( PFP ) and 1‐iodopentafluorobenzene ( IPFB ).…”