Molecular ejection transition in liquid crystal columns self-assembled from wedge-shaped minidendrons

Abstract

A first-order mesophase transition between 4-dendron and 3-dendron columns, resulting from temperature-induced molecular ejection, is discovered and explained via statistical modelling.

Breaking Parallel Orientation of Rods via a Dendritic Architecture toward Diverse Supramolecular Structures

“…Similar to many dendrons systems, [2a] the H HB is as trong interaction, which would drive the molecules to aggregate into core-coronas structures;a nd at the same time,t he parallel arrangement of the rods is assumed to be partially broken to afford the curved interface.T he S SC is al arge contribution to the entropy of the coronas [19] and would increase with increasing available packing space for side chains.T his entropic contribution could approach ac onstant when most molecular conformations of the side chains assume their preferred states;a fter that, af urther increase of packing space for the side chains would induce large void space in coronas,t hus it is unfavorable.C ompared with S SC , the S R of the rods,which is consisting of orientational entropy S Ro and translational entropy S Rt , [6c] has asmaller contribution to the entropy of the coronas.H owever,t his contribution is still important, especially when the side chains have reached their optimum conformations. Similar to many dendrons systems, [2a] the H HB is as trong interaction, which would drive the molecules to aggregate into core-coronas structures;a nd at the same time,t he parallel arrangement of the rods is assumed to be partially broken to afford the curved interface.T he S SC is al arge contribution to the entropy of the coronas [19] and would increase with increasing available packing space for side chains.T his entropic contribution could approach ac onstant when most molecular conformations of the side chains assume their preferred states;a fter that, af urther increase of packing space for the side chains would induce large void space in coronas,t hus it is unfavorable.C ompared with S SC , the S R of the rods,which is consisting of orientational entropy S Ro and translational entropy S Rt , [6c] has asmaller contribution to the entropy of the coronas.H owever,t his contribution is still important, especially when the side chains have reached their optimum conformations.…”

“…[19] For3 OH-2OF n (3,5) and 3OH-4OF n (3,5), when the fan-like molecular shape is assumed to be able to provide enough available packing space for the side chains to afford their most conformations,t he cone-like molecular shape may generate extra void space in coronas.B esides that, the fan-like shape could minimize the exclude volume,t hus also increase the S Rt at the expense of alowering of the S Ro .Inthis case,the fan-like molecular shape would be expected, and the molecules could pack into disclike motifs,which generally allow the formation of columnar structures,c onsistent with our experimental observations. [19] For3 OH-2OF n (3,5) and 3OH-4OF n (3,5), when the fan-like molecular shape is assumed to be able to provide enough available packing space for the side chains to afford their most conformations,t he cone-like molecular shape may generate extra void space in coronas.B esides that, the fan-like shape could minimize the exclude volume,t hus also increase the S Rt at the expense of alowering of the S Ro .Inthis case,the fan-like molecular shape would be expected, and the molecules could pack into disclike motifs,which generally allow the formation of columnar structures,c onsistent with our experimental observations.…”

New Type of Columnar Liquid Crystal Superlattice in Double‐Taper Ionic Minidendrons

“…But on further heating there is an unusual first-order Col hex -Col hex phase transition with an abrupt drop in column diameter,d ue to ac ooperative ejection of the fourth mini-dendron. [53] As in most other single-taper dendrons, in 12-12-12Cs columnd iameter was found to decrease significantly but continuously on heating. [52] At 100 8C m = 4, compared to m = 6i n 1Cs and 2Cs.T he MD annealed model of 12-12-12Cs is shown in Figure 8b.I tc an be seen that, as adjacent columns in 12-12-12Cs are closer together than in 1Cs or 2Cs,t here is more interdigitation of alkyl chains effectively increasing the taper angle of the molecules.…”

“…Another notable difference between the behaviour of single and double‐tapered mini‐dendrons is the fact that while in the former the column area decreases steeply with increasing temperature due to widening taper angle and consequent ejection of surplus molecules from the column, in the current double‐taper compounds the cell area remains constant (Figure ). It has been found previously that in the simple single‐tapered Li 3,4,5‐ tris ‐dodecyloxybenzoate mini‐dendron ( 12‐12‐12Li ) there are also, as in 1Li and 2Li , only μ =3 molecules in a column stratum . The MD‐annealed model of 12‐12‐12Li is shown in Figure S6 alongside that of 1Li for easy comparison.…”

“…As in 1Na and 2Na , in the simple 12‐12‐12Na compound μ =4 above the crystal melting point. But on further heating there is an unusual first‐order Col hex –Col hex phase transition with an abrupt drop in column diameter, due to a cooperative ejection of the fourth mini‐dendron …”