High One-Dimensional Charge Mobility in Semiconducting Columnar Mesophases of Isocyano-Triphenylene Metal Complexes

Abstract

This paper reports the synthesis, liquid crystal behavior, and chargetransport properties in the mesophase of isocyano-triphenylene gold, copper, palladium, and platinum complexes [MX(CNR)] (CNR = 2-(6-(4isocyanophenoxy)hexyloxy)-3,6,7,10,11-pentakisdodecyloxytriphenylene; M = Au, X = Cl, C 6 F 5 , C 6 F 4 OC 10 H 21 , CN;, and [MX 2 (CNR) 2 ] (M = Pd, Pt; X = Cl, Br, I, and M = Pt, X = CN). The thermal and electronic properties of these materials are modulated by the metal fragment. The complexes that display columnar mesomorphism are those that support more than one triphenylene per molecule or those that produce a similar effect by dipole−dipole interactions between the metal groups. These circumstances improve the balance of favorable enthalpic interactions versus unfavorable entropic contributions into a columnar stacking. Hybrid inorganic/organic dual columnar mesophases with high SCLC hole mobility along the columnar stacking, above 1 cm 2 V −1 s −1 , have been found. It is worth noting that the dicyanoplatinum complex displays mesophase phosphorescence based on Pt•••Pt interactions.

Charge Mobility in Discotic Liquid Crystals

“…In this subsection, the last developments regarding the synthesis of novel discotic mesogenic materials will be described. Triphenylene derivatives still remain the most studied compounds and they have been used to develop new materials, testing new side chains, or new cores [ 191 , 192 , 193 , 194 , 195 , 196 ], to be linked with other cores to prepare dyads and triads [ 67 , 197 , 198 , 199 , 200 ] or materials giving segregate columns [ 201 , 202 ]. Triphenylenes were also doped with nanoparticles or used to prepare blends with other mesogenic molecules [ 203 , 204 , 205 ].…”

“…The models proposed for supramolecular organization show that mesophase formation for compounds with a high number of triphenylenes per molecule is favored by the enthalpic stabilization given by the π−π interaction of triphenylenes, while in molecules with only one triphenylene fragment, mesophase formation is favored by the interaction of the high dipole moments deriving from the presence of the metal. Hole mobility depends on mesophase alignment, reaching values up to 10 cm 2 ·V −1 ·s −1 with optimal alignment, among the highest values measured in triphenylene mesogens [ 201 ]. The same group studied the mesomorphic properties of (i) imidazolium salts containing one or two triphenylene units linked through a hexyloxy chain, with metal-complexes as counterions; and (ii) related triphenylene–carbene–metal complexes [ 202 ].…”

Synthesis, mesomorphism, photophysics and device performance of liquid-crystalline pincer complexes of gold(iii)

“…50 Given the increasing interest in the gold(III) system just described and our previous experience with phosphorescent liquid crystals, we have undertaken a study that encompasses the design and synthesis of emissive liquid-crystalline complexes of gold(III) as well as an evaluation of their photophysical response and their performance in solution-processed OLEDs. To the best of our knowledge, the vast majority of known gold-based liquid-crystalline materials 51,52 are linear and based on Au(I) with a C-Au-X or C-Au-C skeleton. As such, the materials reported here represent a new family of metallomesogens and present an opportunity to develop an understanding of the relationship between the molecular structure of the complexes and both liquid crystal and emission properties.…”

Heterocycle Effects on the Liquid Crystallinity of Terthiophene Analogues

“…Liquid crystals (LCs) represent a promising alternative to common crystalline solid organic semiconductors, owing to their ability to self-assemble into ordered self-healing structures capable of uniform alignment over large areas, and with supramolecular order that can be maintained in the solid-state [31,32,33,34,35,36,37]. Although columnar phases have been the most commonly explored liquid crystalline semiconductors, their one dimensional charge conduction is highly susceptible to defects [38,39,40,41,42,43,44]. More recently, smectic LCs have emerged as more attractive candidate materials since their layered structure permits conduction in two dimensions, potentially leading to more consistent performance [45,46,47,48,49].…”