Self‐Assembly in Helical Columnar Mesophases and Luminescence of Chiral 1H‐Pyrazoles

Abstract

Chiral polycatenar 1H-pyrazoles self-assemble to form columnar mesophases that are stable at room temperature. X-ray diffraction and CD studies in the mesophase indicate a supramolecular helical organization consisting of stacked H-bonded dimers. The liquid-crystalline compounds reported are 3,5-bis(dialkoxyphenyl)-1H-pyrazoles that incorporate two or four dihydrocitronellyl chiral tails. It can be observed that the grafting of these branched chiral substituents onto the 3,5-diphenyl-1H-pyrazole core has a beneficial role in inducing mesomorphism, because isomeric linear-chain compounds are not liquid crystalline; this is not the usual scheme of behavior. Furthermore, the molecular chirality is transferred to the columnar mesophase, because preferential helical arrangements are observed. Films of the compounds are luminescent at room temperature and constitute an example of the self-organization of nondiscoid units into columnar liquid-crystalline assemblies in which the functional molecular unit transfers its properties to a hierarchically built superstructure.

Supramolecular Columnar Liquid Crystals with Tapered‐Shape Simple Pyrazoles Obtained by Efficient Henry/Michael Reactions

“…The chiral terminal tails of compound 4e do not impart any observable chiral features to the XRD diffractograms, [4] although an increase in the lattice constant is observedf or 4d,a so ne would expect given the longer chains. On the other hand, 4e has similarl attice constants (only slightly smaller) to 4c.A lthough the chains are shorter for 4e compared with 4c,t his is not relevant for the dimensions of the unit cell.…”

“…The emission wavelength is similar to that found for 3,5-bis(alkoxyphenyl)-substituted pyrazoles. [4,21] The number of terminal chains also influences the fluorescences pectra.T he trisubstituted compounds show ab and at higher wavelengths with much lower quantum yields than the disubstituted compounds.T his observation is consistent with these non-planar compounds having more effective pathways forn on-radiative deactivation by torsional motions.…”

“…The latter approach allows ag reat variety of non-discoid moleculars hapes,s uch as tapered-shapeo nes, to yield columnar liquid crystals. [3] In particular, the 1H-pyrazole heterocycle is able to form intermolecularN H···N interactions and this ability has been successfully exploited to yield columnar mesophases with luminescentp roperties with either disc-like supramolecular dimeric entities [4] or aggregates formed by taperedm olecules. [5] In terms of molecular structure, ac ommon molecular design for columnar liquid crystalsi st oh avea romatic rings substituted with two or three long alkoxy tails (C 6 or longer).…”

Ferroelectrically Switching Helical Columnar Assembly Comprising Cisoid Conformers of a 1,2,3‐Triazole‐based Liquid Crystal

“…Because this is greater than the typical π–π stacking distances, the average stacking direction between the naphthalenyl cores is assumed to be perpendicular to the column axis (Figure a), which is different from that observed in the typical column stacking of discotic LC materials. Based on the XRD results and molecular volume, the number of molecules ( N ) in a column slice can be calculated using the relationship N =(√3a 2 h N A ρ)/2M, where a, h , M, N A , and ρ are the intercolumn distance, column stratum, molecular weight, Avogadro's number, and density (1.0 g cm −3 ), respectively. The calculated N value is approximately 3.…”

Silver Pyrazolates as Coordination‐Polymer Luminescent Metallomesogens

“…[21,32] Based on these observations, the complex emission band of the silver pyrazolates has been tentatively attributed to both intraA C H T U N G T R E N N U N G liA C H T U N G T R E N N U N G gand and ligand-to-metal charge transfer (LMCT) transitions involving the p electronic ground state of the ligand.…”