Mesomorphic donor-acceptor twin molecules with covalently linked sheet-like pentaalkyne and nitrofluorenone sub-units

Abstract

Charge-transfer (CT ) twin mesogens are presented which consist of sheet-like pentayne donor moieties with di erent peripheral substituents chemically linked with nitro substituted uorenone sub-units via¯exible alkyl spacers. A novel plastic rectangular columnar (Colrp) phase is reported for the laterally unsubstituted member of the pentayne based CT twins. The phase is characterized by a three-dimensional crystal-like correlation of ordered columns in a rectangular lattice, while the molecular sub-units are still able to perform relaxation motions.The attachment of peripheral substituents to the pentayne moieties results in a distortion of the three-dimensional positional order and the ® ve-fold alkyl substituted homologues exhibit a rectangular columnar ordered (Colro) mesophase. The rectangular lattice symmetries originate from the chemical linkage of the¯at donor and acceptor parts of the molecules placed in an alternating manner within neighbouring columns, and the regular intracolumnar periodicity is enhanced by charge-transfer interactions within the columns.A further structural modi® cation consists of the incorporation of an asymmetric carbon into the spacer sequence resulting in pentayne based CT-twin mesogens displaying a nematic columnar mesophase with a helical twisting of the columns ( N * col ). Dielectric investigations reveal an unusual dynamic behaviour of the donor± acceptor pentaynes. The glass relaxation process is characterized by the occurrence of two relaxation modes, both following a WLF behaviour, a feature which has not previously been reported to our knowledge for columnar phase-forming disc-like liquid crystal materials.

Optical Storage in Pentaalkinylbenzene Derivatives. Strong Gain Effect by Recrystallization Processes

“…The polar diagram of the diffraction efficiency is displayed as an insert. It has a shape which corresponds roughly to the one reported by us for other liquid crystalline materials. ,,

1 (a and b) Holographic growth curve of compounds 1 and 2 (the nonzero diffraction efficiency at t = 0 results from the background noise originating from the optical setup). (c and d) Holographic growth curve of the doped compounds with TNF.

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“…The role of the liquid crystalline environment has turned out to be two-fold: − it provides a stabilization of the induced orientational order even at temperatures above the glass-transition temperature, and it results in a strong amplification of the optical response. This has become obvious from the observation of a gain effect for materials which could be frozen-in into an amorphous state and became liquid crystalline only on annealing at elevated temperatures. − The storage performed in the amorphous state gave rise to weak optical effects.…”

About Supramolecular Assemblies of π-Conjugated Systems

“…Formation of columnar mesophases from covalently linked donor−acceptor mesogens has been studied, in particular, by Wendorff and Janietz et al, who synthesized, e.g., complexes of electron-rich pentaalkynylbenzene attached directly to TNF. , In these systems strong intermolecular donor−acceptor interactions lead to the formation of highly ordered, columnar mesophases. In further studies elaborating on this work a calamitic azobenzene spacer was used to connect pentaalkynylbenzene or triphenylene ( 197 , Figure ) to TNF.…”

Polarized Photoluminescence from Photopatterned Discotic Liquid Crystal Films

“…Two pentakis[(4-alkylphenyl)ethynyl]benzene derivatives (DLC-1 and DLC-2) were employed here to elucidate orientational behavior of the DLCs spin-cast on the film of 1 , which was obliquely irradiated, accompanied by annealing in advance. Polarized microscope observations revealed that DLC-1 and DLC-2 showed a N D phase in the range of 172−215 and 66−84 °C, respectively.…”