Janus mesophases of matter

ABSTRACT

In ancient Roman religion and myth, Janus is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. He is usually depicted as having two faces looking in opposite directions, one towards the past and the other towards the future. This article is dedicated to Professor BK Sadashiva for his contributions to the science of liquid crystals, and new beginnings in the design and creation of mesomorphic materials.

In the studies of metallomesogens based on copper(II) complexes of β-diketones, Ohta and his colleagues reported the first-established discotic-lamellar phase, in which the board-like complexes are able to form lamellar packing arrangements, and at the same time stacking into columns. Casagrande et al. later prepared synthetically modified beads with one hemisphere being hydrophobic and the other hydrophilic. These particles were considered to be amphiphilic solids, and called Janus Beads. Synthetic Janus Mesogens with supermolecular architectures having one chiral nematic hemisphere and the other with smectic tendencies were made in 2003. These complexes, particles, and supermolecules, were termed Janus to describe the structure of the material. In this article we use Janus liquid crystals to describe a material that combines two different packing motifs in a single uniform phase structure.

Graphical abstract

KEYWORDS:

• Multimesophase
• layers&columns
• TGB
• N_TB
• NS
• antiphases

Acknowledgments

The authors thank Drs Isabel Saez, John Moore, Laurence Abbott, Craig Archbold, Mike Hird, and Robert Lewis for their support and collaborations over the years. We are indebted to the EPSRC for its continued support of our research through the following grants, EP/J007714/1, EP/K039660/1 and EP/M020584/1. The authors also thank QinetiQ for funding an ICASE studentship for RJM, Dr I. Sage for useful discussions, and a special thank you to Professor A. Yoshizawa for a sample of 2-{4-[(R)-2-fluorohexyloxy]phenyl}-5-{4-[(S)-2-fluoro-2-methyldecanoyloxy]phenyl}pyrimidine.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Dedication

Known simply to us as BK, Professor Sadashiva was a very popular liquid crystallographer with the UK Liquid Crystal community. Indeed, Professor Duncan Bruce and I were very fortunate to lead a UK team in a visit to BK’s research home in Banagalore in 2005, see Plate 1. Our visit, funded by the Royal Society of London, was to participate in an India–UK Science Network and to give presentations at a three-day Seminar Series entitled, ‘Recent Trends in Liquid Crystal Research’, at the Raman Institute in Bangalore on the 14–16 of November in 2005. A return Network meeting was held in the University of York on the 10 of July 2007. The meetings at the Raman Institute involved lectures, poster sessions and visits to the research laboratories, and most importantly delightful interactions with the young and enthusiastic scientists coming from a number of institutions. As you know Liquid Crystals is a unique and multidisciplinary subject, in that discoveries in physics, chemistry, biology, and engineering are often brought together under one roof where the transmission of ideas and concepts can move fluidly between the disciplines and researchers. Theories can be put into practice experimentally, visionary discoveries can be probed via theory, and in recent years many of these aspects of research are becoming bound by computation and simulation. This so too short a meeting had all of these aspects, and I don’t think the UK team ever forgot their trip to Bangalore, it meant a lot to them and we were grateful to BK for organizing the Network and the social interactions.

Plate 1. (Colour online) The India–UK Science Network: Three-day seminar on “Recent Trends in Liquid Crystal Science”. Left to Right (back row) Prof AN Cammidge, Dr Krishna Prasad, Prof DW Bruce, Dr Suresh Das, Prof Sriram Ramaswamy, and (front row) Prof Sandeep Kumar, Prof HF Gleeson, Prof VGKM Pisipati, Prof JW Goodby, Prof BK Sadashiva, Prof CT Imrie, and Prof NV Madhusudana.

As a chemist, I take great interest in all chemistry aspects of liquid crystals. In particular, what are (were) the contributions of chemistry to this multidisciplinary subject – why were certain compounds made, how were their molecular architectures designed, how were they synthesised, and how well were they characterized? Privately, while in Bangalore, I asked BK about the discovery of discotic liquid crystals, and I learned that like most chemists he wanted to make disc-like molecules and to see if they were liquid crystalline or not. This seemed to be the seed for the preparation of the hexa-alkanoyloxbenzoates and discotics. Although the targets were straight forward, and having done them myself, their preparations are not easy. Thus, I learned from BK his enthusiasm for making designer molecules, and I greatly appreciated this and his wide contributions to the field. This was emphasised later in York where he gave two masterful presentations on Banana liquid crystals (later called bent-core liquid crystals). We had quite a few discussions on the use of Banana and B phases – he smiled at my despair of the use of Banana and B as mesophase classifiers – after all we already had two B phases.

BK’s wide remit in the synthesis of liquid crystals is probably best summed up in the following two quotations, the first from a UK research report - Chemistry at The Centre: An International Assessment of University Research In Chemistry In The UK, 2009, Chemistry in Britain, November 1985, which identified; ‘One of the exciting opportunities for the future is to use synthesis to prepare molecules that are electronically, optically and perhaps magnetically functional … … ….the initial products of nanotechnology are nanostructured materials prepared by bottom-up synthesis’. And secondly, Professor Sir Jack Baldwin FRS of Oxford University had recognized earlier a similar range of possibilities when he noted that; ‘Chemistry has a strongly creative potential. It can create substances and materials never dreamed of before’. I suggest that BK’s research journey has been reflected in the meaning of Janus. Of beginnings, transitions, duality, doorways, and time, which allowed him too, ‘to create materials never dreamed of before’.

Rest in peace BK. John Goodby FRS, 19.07.21

Additional information

Funding

This work was supported by the Engineering and Physical Sciences Research Council [EP/J007714/1, EP/K039660/1, EP/M020584/1].