A new strategy towards the synthesis of a room-temperature discotic nematic liquid crystal employing triphenylene and pentaalkynylbenzene units

Abstract

A new approach is reported for the design of a room-temperature discotic nematic (N) liquid crystal (LC) dimer consisting of a triphenylene and a pentaalkynylbenzene unit linked via flexible alkyl spacers. The formation of the N phase is realized most likely through folding of the dimeric molecule that prevent stacking between the triphenylene units, as suggested by modelling in the mesophase derived from X-ray scattering results and high-level DFT calculations.

Highly Resolved Morphology of Room‐Temperature Columnar Liquid Crystals Derived from Triphenylene and Multialkynylbenzene Using Reconstructed Electron Density Maps

“…In the present case, the observed Col h phase of the T‐M dyad connected with semi‐flexible spacers is similar to that of the T‐T and T‐PE systems connected with flexible spacer as reported earlier ,. However, we recently reported that T‐M system when connected only via flexible alkyl spacers, exhibits N D phase . This different phase behaviour can be explained as follows: T unit generally self assembles into Col h phase whereas M unit tends to form N D phase.…”

“…When the linking spacer is flexible, then it forms possibly a folded disc and thus minimizes the energy by gaining the entropy while reducing the excluded volume through π‐π interactions between T and M units. These folded discs leads to an improper packing resulting into the formation of a N D phase . On the other hand, T and M unit will tend to be in a plane when they are connected with semi‐flexible spacer because folding will cost much more energy than entropy gain.…”

“…On the other‐hand, multialkynylbenzenes (M) are the most investigated system among the various discotic nematogens where the rotational freedom of ethynyl linkers avoid the stacking of the disks needed for the column formation and hence induce a N D phase . In order to have the desired LC structure and to work with hierarchical structure, dyads and triads of T and T/M/PE have been also explored . But the detailed structure of their self‐assembly is missing.…”

Room‐Temperature Oligomeric Discotic Nematic Liquid Crystals over a Wide Temperature Range: Structure–Property Relationships

“…Recently, we have reported a new approach for the design of a room‐temperature N D LC dimer consisting of a TP and a PA unit linked through flexible alkyl spacers. The formation of the room‐temperature N D phase is likely due to folding of the dimer, which prevents π–π stacking among the composite disc units . In this communication, we have developed another new strategy to obtain a room‐temperature N D phase over a wide temperature range by connecting four PA units to an azobenzene core through flexible alkyl spacers.…”

Supramolecular Self‐Assembly of Ionic Discotic Liquid Crystalline Dimer with DNA at Interfaces

“…For discotic dimers, the edge‐on conformation could be of two types, namely, folded‐ and unfolded‐form as shown in Figure C. Particularly, if the two discotic cores of the dimer are connected by flexible spacer, they tend to fold due to the strong π‐π interactions . In the present work, the TpImTp dimer molecule is symmetric and the experimentally observed A o values only indicate an edge‐on conformation without clarifying whether or not it is folded.…”