Chromonic mesophases

Current Opinion in Colloid and Interface Science 8 (2004) 480–490 

Chromonic mesophases 

John Lydon 

University of Leeds, The School of Biochemistry and Molecular Biology, Leeds LS2 9JT, UK 

Abstract 

Over the last 10 years, there has been a growing acceptance of the concept of chromonic phases and a wider recognition that 

they form a well-defined family of lyotropic liquid crystalline phases, with a package of properties distinct in almost every aspect, 

from those of conventional amphiphiles. New chromonogenic compounds have appeared and new technological uses for chromonic 

systems are being actively explored. Recent promising investigations include the synthesis of a chromonic dye, C.I. Direct Blue 

67, which has an N phase of high order parameter and which can be dried down to give well-oriented films of solid. When dried 

down on a ‘command surface’ of photoaligned substrate this can produce a highly patterned film. The use of chromonic phases 

in the construction of compensating plates for improving the viewing characteristics of twisted nematic displays has been explored. 

Although this technology may not be suitable for commercially exploitation in its present form, the success of the devices is 

significant. It is suggested that current studies of the way in which the temperature range of thermotropic discotic mesophases is 

enhanced in 1:1 CPI mixtures may well lead to improved formulations for chromonic dyes. It is predicted that the marriage of 

chromonic phase technology with current biochemical analytical techniques will give rise to a new generation of medical 

diagnostic tests. 

2004 Elsevier Ltd. All rights reserved. 

1. Introduction 

About two decades ago it was becoming clear that 

there is an extensive and well-defined family of lyotropic 

mesogens with properties distinct from those of conventional 

amphiphiles. This family consists of various 

drugs, dyes, nucleic acids, antibiotics, carcinogens and 

anticancer agents. In almost every respect the properties 

are different to those of ordinary lyotropic mesogens of 

the soapydeterergentyphosphilipid type. The molecules 

have aromatic rather than aliphatic structures. They are 

rigid rather than flexible and planar disc-like or planklike, 

rather than rod-like. The hydrophilic solublising 

groups are disposed around the periphery of the molecules 

rather than at one end. The molecules aggregate 

in solution, not into micelles, but into columns. They 

have distinctive optical textures (involving characteristic 

types of paramorphosis). Thermodynamic measurements 

indicate that the driving force for the aggregation is 

enthalpic rather than entropic. Their phase diagrams 

tend to be of the peritectic rather than eutectic type. 

They do not show cmc’s or Krafft points. These are the 

chromonic mesophases 

E-mail address: j.e.lydon@leeds.ac.uk (J. Lydon). 

This review is intended to be read as an update of 

●● 

two previous papers. The first w1 x, in The Handbook 

of Liquid Crystals, gives details of the prehistory of 

chromonic phases, the patterns of molecular aggregation 

in N an M phases and NyM phase diagrams and includes 

a description and analysis of characteristic optical textures. 

The second w2 x, in this journal 5 years ago, 

●● 

described the newer brickwall and chimney types of 

aggregation encountered in some chromonic dyeywater 

systems and discussed the extension of the Israelachvili 

approach from lyotropic amphiphile systems to chromonics 

(Figs. 1 and 2). 

The recent developments discussed in this review fall 

into three categories. The first concerns the use of an 

optical alignment technique to produce detailed patterns 

of alignment in dried down films of dyes. The second 

concerns the experimental use of chromonic phases in 

compensating plates to improve the performance of the 

standard twisted nematic display devices. The third 

concerns CPI mixtures—a theme of current interest in 

thermotropic discotic systems, which I predict will 

become of importance in the future technological exploitation 

of chromonic systems. 

1359-0294/04/$ - see front matter 2004 Elsevier Ltd. All rights reserved. 

doi:10.1016/j.cocis.2004.01.006

J. Lydon / Current Opinion in Colloid and Interface Science 8 (2004) 480–490 

481 

Fig. 1. The Structures of Chromonic N and M Phases. Chromonic mesogens can be regarded as being insoluble in one dimension. They tend to 

aggregate face-to-face, producing a variety of stacked structures. The classic chromonic phases are the nematic, N phase and the hexagonal, M 

phase. In both of these, the molecules are stacked in columns. In the N phase, these lie in a nematic array (i.e. the columns are more or less 

parallel, but there is no positional order and there is no orientational order of the columns about their long axes). In the M phase, the columns 

lie on a lattice with statistical hexagonal symmetry and have long-range order. Other chromonic structures have been identified by Tiddy et al. 

and Harrison et al. where the molecules are aggregated into brickwork patterns or cylindrical chimneys w2,18,19x. 

2. Outline of chromonic phase structure and 

properties 

The name chromonic was derived from the bischromone 

structure of the widely marketed anti-asthmatic 

known in the UK as INTAL and in the US as 

Chromolyn w3–10x—by no means the first mesogen of 

this type to be reported—but one of the most extensively 

studied. It was considered (by its creator at least) to be 

a particularly good name because of the fortuitous 

combination of connotations of the word, with both 

colour (with reference to dyestuffs) and with chromosomes 

(with reference to nucleic acids). 

Chromonic mesophases are the lyotropic counterparts 

of the discotic mesophases-and there are some parallels 

in their history. In both cases, the definition of the 

concept came far later than one would have expected. 

The so-called ‘carbonaceous phases’ had been known 

and characterised by the coking industry for decades 

and there were predictions of ‘negative nematic’ liquid 

crystalline phases years before Chandrasekhar’s classic 

work. Similarly, references to the aggregation of dye 

molecules, stacking like piles of pennies or packs of 

cards were scattered in the dye chemistry literature for 

almost a century. Terms such as H- and J-aggregates 

were widely used in the industry—but there was scarcely 

ever a mention of liquid crystalline properties. 

In many aspects, chromonic systems are closer to 

thermotropic systems than to conventional amphiphiles. 

In both cases, the driving force causing liquid crystalline 

phase formation is the face-to-face aggregation of molecules 

forming columns—and the geometrical aspects 

of the packing of these columns are more or less the 

same in the two cases—the difference being that in one 

case the columns lie in a sea of alkyl chains and in the 

other, they lie in a sea of water. I had expected that by 

now, chromonic counterparts of all of the thermotropic 

discotic phases would have been found. Bearing in mind 

the extensive literature of the dye industry concerning 

tilted stacks of dye molecules (J-aggregates), I find it 

surprising that there are, as yet, no well-authenticated 

tilted chromonic systems. 

In general, there is a strong tendency for chromonic 

molecules to aggregate into columns, even in very dilute 

solution—just as conventional lyotropic mesogens form 

micelles before a mesophase is formed w11,12x. 

Although there may be a threshold concentration before 

significant aggregation begins to occur, there is no 

specific optimum column length and, therefore no analogue 

of the critical micelle concentration (cmc) of 

Fig. 2. A snapshot plan view of the chromonic M phase. The array 

shown in this sketch has orthorhombic symmetry – but the rotational 

disorder of the columns between the three possible orientations (as 

indicated for the central column) leads to the phase having overall 

hexagonal symmetry. The hexagonal lattice spacing is approximately 

half the length of the molecule plus half the width of the molecule 

plus the thickness of the interlying water w1,4,10,29x. For the dye 

molecule shown in Fig. 3, this is approximately 24 A. ˚

482 J. Lydon / Current Opinion in Colloid and Interface Science 8 (2004) 480–490 

conventional amphiphiles. The term ‘isodesmic’ (first 

used in the study of the aggregation of nucleic acids in 

solution) has been applied to the steady build up of 

chromonic aggregates where the addition or removal of 

one molecule to a stack is always associated with the 

same increment of free energy w13,14x. This is in direct 

contrast with the situation for conventional amphiphile 

association, where the micelle represents a free energy 

minimum—and there is a cost to the system in having 

either larger or smaller units. 

A further fundamental distinction between conventional 

amphiphile and chromonic systems concerns what 

happens at the lower temperature limit of mesophase 

formation. In conventional amphilphiles, there are two 

micro-phase regions; the aqueous and the hydrophobic, 

aliphatic parts. As the temperature is lowered, the alkyl 

chain motion in the hydrophobic region usually freezes 

out, forming a gel phase. The system becomes too brittle 

to be able to pack into the micelles required for 

mesophase formation. This gives a lower temperature 

limit characterised by its Krafft temperature. In chromonic 

systems the opposite happens. Because of the 

absence of alkyl chains in chromonic systems (or at 

least the absence of significant lengths of alkyl chains), 

chromonic systems do not show a Krafft point and the 

lower temperature is limit is marked by the appearance 

of ice—usually a few degrees below 0 8C. Note that 

there is evidence that one can access monotropic chromonic 

phases at sub-zero temperatures by adding an 

antifreeze to the system w7,9x. 

Misciblity is a feature of liquid crystalline systems – 

and in general, an understanding of the rules which 

govern miscibility is crucial to our understanding of the 

factors which determine the dynamics of each type of 

mesophase. The chromonic analogue of miscibility is 

intercalation where guest molecules can be accepted 

randomly into chromonic stacks. Although there have 

been no extended systematic studies of chromonic miscibility 

it appears that this is as widespread as miscibility 

in other mesophase systems w15x. 

There is another related pattern of behaviour of 

chromonic mixtures (which is discussed in more detail 

below). This occurs where there is a strong preference 

for an ABAB alternating arrangement of the two components 

in every stack w47–53x. This occurs to such a 

pronounced extent that the alternating column must be 

regarded as the structural unit of the phase. Since at 

least some of these CPI ‘compounds’ give mesophases 

with enhanced stability (and since the aromatic cores of 

the compounds in both families of mesophase are 

similar), it is an obvious suggestion that the search for 

similar effects in chromonic systems would be 

worthwhile. 

Chromonic systems can be doped with small soluble 

chiral compounds to give a chiral N phase (in an 

Fig. 3. The molecular structure of C.I. Direct Blue 67. This new dye 

forms a chromonic N phase of high order parameter and which can 

be dried down to give an aligned solid film. Matsunaga et al. w29x 

have shown that a highly patterned film can be produced by drying 

down the N phase on a photaligned command substrate as sketched 

in Fig. 5. 

analogous way to the chiral doping of thermotropic 

nematics). Since the twist produced is proportional to 

the concentration of the dopant, this property has been 

proposed as a practical assay for chiral compounds 

w7,9x. A new exploitation of the chirally-doped N phase 

is in compensating devices for TN cells as described 

below w38–40x. 

3. New chromonic materials 

The range of compounds which form chromonic 

phases now includes xanthoses (used as antiasthmatic 

drugs, azo dyes, cyanine dyes, nucleic acids (guanosine 

derivatives) and perylenes w16–26x. 

Over the last few years, reports of new chromonic 

mesophases have grown from a trickle to a stream. 

These include a report of a new metallo-mesogen and 

excitingly, a non-aqueous chromonic system (where the 

solvent is dimethyl formamide) w27,28x (Fig. 3). 

Significant amongst new chromonic materials is the 

● 

azo dye, C.I Direct 67 w29 x. This shows typical NyM 

phase behaviour promises to become a useful new 

chromonic compound. The chromonic phases formed by 

aqueous solutions of this dye were investigated by means 

of temperature-controlled X-ray diffraction, polarised 

light microscopy and UV–visible spectroscopy. The dye 

molecules form columnar aggregates, even at low concentrations. 

The structural study gave results very similar 

to those of earlier work on the INTALywater system 

w5,6,10x. As one would expect, the stacking repeat was 

3.4 A ˚ (and was found to be independent of concentration 

and temperature). The diameter of the column was 

found to be comparable with the length of the molecule—suggesting 

that the column is a unimolecular 

stack. One interesting feature of this investigation was 

the observation that the addition of a small amount of 

anionic surfactant (0.01% by wt.) was found to enhance 

the stability of the nematic phase (at the expense of the


483 

Fig. 4. The production of an aligned dye coated polymer film using 

a ‘command plate’ produced by the Weigert effect. A spin-coated film 

of the azo compound is photaligned with a beam of plane polarised 

light to produce a ‘command plate’. 

M phase). Clearly at this concentration there is no 

suggestion of the added amphiphile having a direct 

structural effect on the mesophase such as coating the 

columns. The effect must be more subtle. Perhaps in 

some way it stabilises column ends or simply alters the 

chemical potential of the counter ions. 

Over the last 10 years, a photoalignment approach 

has been developed which appears to have the potential 

for achieving this w30–37x. This technique utilises the 

Weigert effect. This is the sensitivity of some photohemical 

reactions to the orientation of the plane of polarised 

light striking the molecule. Reactions for which the 

Weigert effect has been observed include photobleaching, 

photodimerization and photoisomerism. In the photoalignment 

of photoisomerisable molecules the final 

state of the sample has the molecular director aligned 

normal to the electric vector of the incident light (Figs. 

4 and 5). 

Azobenzene has been a favourite compound for producing 

aligned films using the Weigert effect. Unfortunately, 

it is only weakly absorbing in the visible 

wavelengths range and it is, therefore by no means 

ideal. There is a way round this problem, however. It 

has been found that a film of phoaligned azobenzene 

molecules is able to epitaxially align liquid crystalline 

phases. The photoaligned substrate can, therefore be 

used as a ‘command surface’, which is in turn able to 

direct the alignment if the mesophase. Photoinduced 

alignment of this kind was first demonstrated with 

thermotropic mesophases (using films of azodoped polymer, 

polymers with azobenzene side groups or polymers 

with cinnamic acid side groups). However, it also works 

for lyotropic phases and can be used to align the 

chromonic N phase. 

● 

In their recent paper, Matsunga et al. w30 x describe 

the production of a patterned film of dye using this 

approach. They used a striped template command surface 

prepared from the photoinduced alignment of a 

polyamide with azo side-groups. The chromonic N phase 

of the dye, C.I. Direct Blue 67 is aligned by this surface 

and then dried down to give a patterned film. They 

4. The production of patterned dye films 

In the production of optical elements such as polarisers, 

retarders and optical compensators, it is necessary 

for us to be able to control the alignment of birefringent 

material embedded in (or deposited on) a film. A variety 

of manufacturing processes have been tried, including 

classical mechanical methods such as stretching the 

film, shearing, rubbing the surface and newer approaches 

such as electric field poling. The disadvantage of all of 

these approaches is that they are only able to produce 

surface films with same alignment over the entire area 

of film being treated. What would be much more 

desirable is a technique which could align small areas 

of film in different orientations, ultimately giving us the 

ability to align individual pixels in any required 

orientation. 

Fig. 5. The epitaxial alignment of a chromonic N phase by a photoaligned 

command plate. (redrawn from Ref. w30x).


Fig. 6. Conventional (uncompensated) twisted nematic cells in the on 

and off states. There are two forms of the twisted nematic cell: normally 

white (NW) and normally black (NB) cells – the difference 

lies only in the orientation of the upper polarising layer plate. 

The twisted nematic (TN) device continues to dominate 

the flat panel liquid crystal display market. However, 

it is not without its shortcomings. The 

characteristics of an ideal device are high contrast, a 

wide viewing angle, good colour rendition and a completely 

achromatic dark state. The standard (uncompensated) 

TN device fails to live up to every one of these 

ideals. In particular, the phenomenon known as ‘greyscale 

inversion’ can be severe. This arises where the 

contrast between ‘on’ and ‘off’ areas falls to zero and 

is then reversed, as the viewing angle is changed. 

The defects of the standard TN cell can, in some 

measure, be corrected by the addition of a compensator. 

This is an optical system, which matches the optical 

characteristics of the sample and reduces the contrast 

loss as the viewing angle is increased. An ideal compensating 

device would ‘correct’ the optics of both the 

‘on’ and ‘off’ states, but this is an over-ambitious target 

at the present time. Current compensators are passive 

devices, which are designed to correct only the more 

critical of the two states of the device. In an uncompensated 

TN cell there is both leakage of light through the 

dark state and a decrease of intensity of the light state. 

However, the effects of these deficiencies are not symmetrical 

and the leakage of light through the dark state 

is the more serious. Because of this, compensators are 

specifically designed to improve only the dark state 

optics. 

The structures of the two variants of the standard (i.e. 

non-compensated) TN cell are shown in Fig. 6. In a 

cell in the ‘off’ state, the twisting molecular alignment 

rotates the plane of polarisation of the light through 908. 

In the ‘on’ state, the molecules are realigned to give a 

homeotropic state where the molecular axes lie perpendicular 

to the cell surface. This arrangement does not 

change the polarisation state of the light. There are two 

geometries that are used in these devices—with the two 

polarisers lying either parallel or perpendicular. The 

parallel arrangement gives a ‘normally black’ (NB) 

device in the absence of a field and the perpendicular 

arrangement gives a ‘normally white’ (NW) device. 

Compensators have, therefore been devised to improve 

the optics of the ‘off’ state of the NB device and the 

‘on’ state of the NW device. 

were able to produce a solid dye film consisting of 

alternating 300-mm wide rows of orthogonally aligned 

dye material with impressively sharp-edged resolution. 

5. The use of planar and twisted lyotropic chromonic 

liquid crystal cells as optical compensators for twisted 

nematic cells 

Fig. 7. A more accurate view of the mesophase alignment of the NW 

cell in the ‘on’ mode. To a first approximation, the applied field aligns 

the mesophase in a homeotropic pattern as sketched in Fig. 6. However, 

molecules near to the surfaces tend to retain a parallel alignment 

and the phase adopts a complex splay pattern shown.


485 

7. Compensating a normally white cell 

For a NW cell, the situation is more complex. In the 

dark ‘on’ state the director field is not perfectly homeotropic 

and the arrangement sketched in Fig. 6 is only 

an approximation to reality. In practice, the situation is 

more like that sketched in Fig. 7 where the molecules 

near to the upper and lower substrate surfaces retain a 

parallel alignment and, as the director field curves 

towards the homeotropic region in the centre, there is 

appreciable splay distortion. A plate compensating specifically 

for this splay has been developed by Fuji. 

In addition to the splay distortion, the optics require 

correction for birefringence and Lavetrovitch et al. 

● 

w40 x have explored the use of chromonic cells to 

compensate for the birefringence and twist. The layout 

of their complete device is shown in Fig. 9. 

Fig. 8. The design of a compensated NB cell (Lavrentrovich et al. 

w40x). Compensators have been added to improve the optics of the 

dark ‘off’ state. The twisted compensating cell is filled with a chirally 

doped N* phase, the compensating A-plate contains a parallel-aligned 

chromonic mesophase. (redrawn from Ref. w40x). 

6. Compensating a normally black TN cell 

The root cause of the optical problems of a TN cell 

is the large positive birefringence of the cell. One can 

improve the optical performance of a NB display by 

compensating this with a passive retarder. The compensating 

plate should have negative birefringence and a 

twisted structure that mirrors that of the cell in the ‘off’ 

mode. An early attempt at constructing a compensator 

with these properties consisted of several superposed 

polymer films with negative birefringence. These were 

stacked in a twisted arranged to match the twist director 

twist of the cell in the ‘off’ state. More sophisticated 

compensators have been constructed by Laventrovitch 

● 

et al. using liquid crystalline phases w38–49 x. To 

counteract the positive birefringence of the nematic 

phase, phases with negative optical anisotropy are 

required. This suggests the use of thermotropic discotic 

and lyotropic chromonic phases—and both have been 

tried. 

The design of an experimental compensated NB TN 

● 

cell devised by Laventovitch et al. w40 x is shown in 

Fig. 8. Note that this employs a combination of a planar 

N-phase chromonic cell and a twisted N* chromonic 

cell to match the uncompensated optics. 

Fig. 9. The design for a compensated NW cell (Lavrentrovich et al. 

w40x). Compensators have been added to improve the optics of the 

dark, ‘on’ state. The Fuji plates compensate for the splay shown in 

Fig. 7. The compensating A-plates contain a parallel-aligned chromonic 

mesophase. (redrawn from Ref. w40x).


I have given prominence to the use of chromonic 

compensators in this review. This was not done, because 

I believe that devices of the kind described using the 

chromonic solutions are immediately feasible for largescale 

commercial production. The narrow temperature 

range of the chromonic phase used would alone make 

this impracticable. The importance lies in the way it 

stresses the versatility of this family of mesophases. 

8. Complementary polytopic interaction (C.P.I.) in 

discotic systems 

The so-called p–p interactions which hold chromonic 

molecules face to face have been discussed by Hunter 

et al. w41–43x and Bates and Luckhurst w44x. They argue 

that these interactions are in fact a combination of van 

der Waals forces and electrostatic interactions and that 

no specific properties of p systems need be invoked. In 

recent studies of thermotropic columnar mesophases, in 

the search for enhanced electronic conductors, a phenomenon 

has been encountered which suggests that in 

certain cases, two different molecules can form 1:1 

‘compounds’ with enhanced mesophase-forming properties 

w45–53x. In these cases, the structural unit is 

thought to be the (AB) n column. The reason why these 

alternating columns are ‘better’ mesogenic units than 

those of either of the two separate species is not 

immediately evident. Some form of ‘bonding’ must be 

occurring between the two types of molecules, which is 

not describable in classical chemical terms. The interaction 

appears to be more subtle than a simple covalent, 

hydrogen bonding or electrostatic effect. There is no 

evidence that the electronic structure of either molecule 

is significantly disturbed and there is no detectable 

charge-transfer interaction. The explanation for the complementary 

nature of the two types of molecule appears 

to lie in the sum total of a large number of atom-byatom 

van der Waals type interactions. The term complementary 

polytopic interaction (C.P.I.) has been coined. 

Computer modelling of the interactions between the two 

types of molecule in such systems has been carried out 

using the XED program and the results appears to 

confirm this view. 

The two component phase diagram of two compounds 

which interact in this fashion, recently reported by 

● 

Boden, Bushby and Lozman w53 x is shown in Fig. 10. 

Note that one of these compounds is mesogenic on its 

own, and the other, although having a similar overall 

structure (with a polyaryl core and a halo of alky 

chains) is not. The thin vertical region at the centre of 

the diagram represents the 1:1 C.P.I. compound. The 

extreme narrowness of this single phase area implies 

that there is a very positive interaction between the two 

types of molecule and that we are dealing with a system 

qualitatively different to one based simply on the mutual 

solubility of the two component. Note in particular, that 

the discotic columnar temperature range is enhanced in 

both directions, with the mesophase extending to higher 

and lower temperatures than those of the pure mesogenic 

component. The result of computer modelling the docking 

of an ABA unit of the column using the XED 

program is shown in Fig. 11. 

The reason for highlighting a property of thermotropic 

mixtures in this review is that I can see no reason why 

such effects should not arise in chromonic systems— 

especially since in some cases, the core polyaryl parts 

of the molecules are the same. In the past, the suggestion 

that it ought be possible to convert intransigent, insoluble 

dyes into conveniently soluble mesophases by the 

addition of some magic colourless agent was greeted 

with dismissive scepticism by the (British) dye industry. 

Perhaps it now looks one increment more plausible. 

9. The future 

The development of chromonic mesohase studies has 

not proceeded in the way I had expected. Bearing in 

mind the large industry concerned with the production 

and use of dyestuffs for printing fabric and paper and 

the apparently widespread occurrence of chromonic 

phases amongst dyes, I had expected that over the last 

decade there would have emerged a large literature 

concerned with enhancing the solubility properties (i.e. 

the mesophase-forming properties) of dyes, the investigation 

of mesophase enhancing mixtures, the fine tuning 

of colour by the addition of non-dye chromonic additives, 

the specalist use of the alignment of mesophases 

on prepared surfaces and with electric and magnetic 

fields for printed material—perhaps for high grade 

security printing such as banknotes, credit cards and 

identification. As far as I am aware, little of this has 

occurred. However, the production of aligned dye films 

has materialised (albeit requiring a command surface). 

In the previous review, I referred to two grails. The 

first was of these is the production of cheap electrically 

conducting organic material, the second, a viable lightharvesting 

device. With the development of techniques 

to control the alignment of chromonic phases to produce 

multilayer stacks of aligned phases w54x, and to produce 

highly-aligned films by drying down chromonic phases 

(enabling circuits to be produced by ink jet printer), 

both appear to have been brought a step closer. 

The use of chromonic phases as compensating plates 

for TN devices came as a surprise—but since an 

optically negative nematic phase was required, there 

were not a lot of alternative systems to choose from. 

Polymer films and discotic and chromonic mesphases 

are the obvious three—and all have been investigated. 

The major distinction between chromonic phases and 

thermotropic phases is of course the fact that they are


487 

Fig. 10. The production of ABAB stacks by complementary polytopic interactions (CPI). In some mixtures of thermotropic discotic and ‘near 

discotic’ compounds, it appears that the 1:1 mixture gives a columnar phase with a wider temperature range (and enhanced conductivity and 

photoconductivity) than that of either of the two separate compounds. It is presumed that the two molecules complement each other in some way 

and that the enhanced stability of the mesophase is due to the enhance stability of the ABAB columns. This example of the CPI effect is for a 

binary system of a mesogen, hexaalyltryphenylene(HAT6) – based derivative and the non-mesogenic compound, hexakis(4-nonylphenyl)dipyrazino 

w2,3-f:2.3.hxquoinoxalene( PDQ9). The nematic phase of the CPI 1:1 mixture occurs as a narrow vertical band at the centre of the 

phase diagram. The shaded area at the bottom of this band indicates where the chromonic N phase of the CPI compound is in a glassy state. 

(redrawn from Ref. w53x).


proposed). However, there are still books being produced 

which purport to give a broad overview of ‘soft 

matter’, which omit all mention of chromonics. A single 

large-scale commercial application of chromonics will 

of course change this picture overnight. The widespread 

technological use of chromonic systems has not yet 

materialised, but the continuing discovery of unique 

properties and versatility of these systems promises 

much. I would hazard the guess that wherever nanotechnology 

takes us, the liquid crystalline state will never 

be far away—and chromonic systems will have something 

vital to offer. 

Acknowledgments 

I am indebted to Richard Bushby, Owen Lozman and 

to Gordon Tiddy for their continuing encouragement. 

References and recommended reading 

● of special interest 

●● of outstanding interest 

Fig. 11. Orthogonal views of the optimum stacked columnar structure 

of a sequence of HAT1–PDQ1–HAT1 molecules as predicted by the 

XED program. The material in this figure is taken from Ref. w53x. 

The XED program is described in Refs. w41–43x and Vinter JC, Saunders 

MR: Ciba F Symp 1991, 158:249–265, Vinter JC: J Comp-Aid 

Mol Des 1994, 8:653–668, Vinter JC: J Comp-Aid Mol Des 1996, 

10:417–426. 

‘water based’. This should makes possible a marriage 

between established display technology and established 

biochemical techniques. I foresee the diagnostic biomedical 

tools of the next century operating via a combination 

of liquid crystal display technology and biochemical 

recognition. 

10. Conclusion 

The recognition of chromonic mesophases as an 

important and distinct class of lyotropic mesophases is 

still patchy. Papers are now appearing where the term is 

used without the authors feeling the need to define it 

(and to refer to the literature where the word was first 

w1x 

●● 

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Chromonic mesophases

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