Design of Chemoresponsive Liquid Crystals through Integration of Computational Chemistry and Experimental Studies

Abstract

We report the use of computational chemistry methods to design a chemically responsive liquid crystal (LC). Specifically, we used electronic structure calculations to model the binding of nitrile-containing mesogens (4′-n-pentyl-4biphenylcarbonitrile) to metal perchlorate salts (with explicit description of the perchlorate anion), which we call the coordinately saturated anion model (CSAM). The model results were validated against experimental data. We then used the CSAM to predict that selective fluorination can reduce the strength of binding of nitrile-containing nematic LCs to metalsalt-decorated surfaces and thus generate a faster reordering of the LC in response to competitive binding of dimethylmethylphosphonate (DMMP). We tested this prediction via synthesis of fluorinated compounds 3-fluoro-4′-pentyl[1,1′-biphenyl]-4-carbonitrile and 4-fluoro-4′-pentyl-1,1′-biphenyl, and subsequent experimental measurements of the orientational response of LCs containing these compounds to DMMP. These experimental measurements confirmed the theoretical predictions, thus providing the first demonstration of a chemoresponsive LC system designed from computational chemistry.

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

“…So far, the discussion has focused on pure LC systems, where the surface‐driven LC transitions are triggered by the interaction of gas analyte molecules and chemical functionalities of the surface or by topography surface features. In this section, we will discuss examples of nematic systems doped with affinity molecules that can either enhance or induce an orientation to the LC, [ 111,112,117,138 ] or, more interestingly, interact with the gas analyte [ 139,140 ] ( Table 3 ). The most prominent example of the latter case has been demonstrated by Ding and Yang [ 139 ] where a gas sensor for butylamine vapor detection was developed.…”

“…Pal et al [ 141 ] and more recently Szilvasi et al [ 138 ] have studied mesogenic mixtures containing specific moieties and their performance in response to the volatile compound DMMP. Pal et al [ 141 ] studied a series of mixtures of 5CB with 4‐pentyl‐3′,4′‐dicyanobiphenyl (DCB), a non‐LC benzonitrile‐based molecule which contains two nitrile groups, with varying concentrations from 0.9 to 2 wt% in DCB.…”

“…However, the LC mixtures exhibited a slow response to the presence of DMMP vapors (roughly 180 s), when compared to pure 5CB (15 s). Szilvasi [ 138 ] has combined computational chemistry and organic synthesis studies, showing that the selective fluorination of 5CB molecules can reduce the binding strength of their nitrile group to metal salt decorated surfaces. This hypothesis was tested on a mixture of pure 5CB and an ortho ‐fluorine modified 5CB (named FCB, which does not exhibit LC behavior) deposited on a variety of different surfaces decorated with perchlorate salts of Fe 3+ , Al 3+ , Ga 3+ , La 3+ and Zn 2+ .…”

Redox‐Triggered Orientational Responses of Liquid Crystals to Chlorine Gas

“…The first step in our approach used computational chemistry methods to select metal cations that exhibit oxidation‐state‐dependent binding interactions with mesogens . Specifically, we systematically studied the binding of benzonitrile (PhCN), a surrogate for the common mesogen 4‐cyano‐4′‐pentylbiphenyl (5CB; Scheme ) with a range of metal cations (as perchlorate salts; Table ).…”

Redox‐Triggered Orientational Responses of Liquid Crystals to Chlorine Gas

“…We illustrate the approach using Cl 2 gas.Thef irst step in our approach used computational chemistry methods to select metal cations that exhibit oxidation-state-dependent binding interactions with mesogens. [26][27][28][29] Specifically,w es ystematically studied the binding of benzonitrile (PhCN), asurrogate for the common mesogen 4-cyano-4'-pentylbiphenyl (5CB;S cheme 1) with ar ange of metal cations (as perchlorate salts;T able 1). Ther esults Scheme 1.…”