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.

Graphene oxide-based nanocomposites (NCMs) exhibit diverse photonic and biophotonic applications. Innovative nanoengineering using a task-specific ionic liquid (IL), namely, 1-butyl-3-methyl tetrafluoroborate [C 4 mim][BF 4 ], allows one to access a unique class of luminescent nanocomposites formed between lanthanide-doped binary fluorides and graphene oxide (GO). Here the IL is used as a solvent, templating agent, and as a reaction partner for the nanocomposite synthesis, that is, “all three in one”. Our study shows that GO controls the size of the NCMs; however, it can tune the luminescence properties too. For example, the excitation spectrum of Ce 3+ is higher-energy shifted when GO is attached. In addition, magnetic properties of GdF 3 :Tb 3+ nanoparticles (NPs) and GdF 3 :Tb 3+ -GO NCMs are also studied at room temperature (300 K) and very low temperature (2 K). High magnetization results for the NPs (e.g., 6.676 emu g –1 at 300 K and 184.449 emu g –1 at 2 K in the applied magnetic field from +50 to −50 kOe) and NCMs promises their uses in many photonic and biphotonic applications including magnetic resonance imaging, etc.

Solid-state luminescent materials which are sensitive to external stimuli are of enormous importance due its potential for application as smart responsive materials and devices. Here we report the changes in...