Stabilization of the Columnar Mesophase of Perylenediimide by Racemic Triple Tails

Abstract

Whereas perylene tetracarboxdiimides derived from amino-n-alkanes if at all only show monotropic (thermodynamically unstable) mesogenic self-assembly, the hexagonal columnar liquid crystalline state can be stabilized over a broad temperature range with doubly branched, doubly racemic alkyl residues. An improved tendency to homeotropic surface orientation is observed, and the orientation of the liquid crystalline domains is maintained upon cycling through the crystalline state at room temperature.

From 1,4‐Phenylenebis(phenylmaleate) to a Room‐Temperature Liquid‐Crystalline Benzo[ghi]perylene Diimide

“…Tetraesters of polycylic arenetetracarboxylic acids tend to form columnar liquid crystals that are of interest as anisotropic charge‐transport materials . The corresponding diimides with racemic secondary alkyl residues have recently been found to also form such mesophases, in spite of the presence of only two branched flexible substituents (Scheme ). Imides are of particular interest since they are more stable towards hydrolysis than esters, and the electron‐withdrawing effect of imide groups is considerably stronger in six‐membered‐ring diimides (like perylene diimide (PDI) 1 ) than in five‐membered‐ring diimides (like 2 ).…”

“…The corresponding diimides with racemic secondary alkyl residues have recently been found to also form such mesophases, in spite of the presence of only two branched flexible substituents (Scheme ). Imides are of particular interest since they are more stable towards hydrolysis than esters, and the electron‐withdrawing effect of imide groups is considerably stronger in six‐membered‐ring diimides (like perylene diimide (PDI) 1 ) than in five‐membered‐ring diimides (like 2 ). Thus the latter may be considered as electron donors with respect to the former; all‐imide donor–acceptor junction devices may thus be envisaged …”

Columnar Liquid‐Crystalline Dibenzopentacenodithiophenes by Photocyclization

“…Methanol (50 mL) was added and the precipitate was filtered off, purified by column chromatography on silica in chloroform containing 1% of ethanol and recrystallized twice from 2:1b utanol/ isopropanol. Yield:9 4mg( 1051.5 gmol À1 ,4 0%)o fr ed solid; Te tracarboxdiimide 7b was obtained from 9 and 7-amino-5-ethyltetradecane hydrochloride [15] by following the preceding procedure, with recrystallizations from butanol. Yield:7 7mg (1051.5 gmol À1 ,3 3%)o fr ed solid.…”

“…With the aim to improve the mesogenic behavioro f7,w e increased the racemic disorder of the alkyl substituents by using the doubly racemic triple-tail amine 7-amino-5-ethyltetradecane to give the corresponding diimide 7b.T he same doubly branched 1-(2-ethylhexyl)octyls ubstituent has recently allowed us to obtain PDI 5 with ab road columnar mesophase range, whereas the corresponding PDI with 1-hexyldecyl groups showed no mesophasea tall. [15] The mesophase of 7b ( Figure 2) clears at 309 8Ct ot he isotropic liquid,t hat is, 38 8Ch ighert han isomeric 7a.T he doubly branched alkyl moieties thus stabilize the mesogenic self-assembly of 7 significantly against the loss of long-range columnar order upon heating.U pon cooling, the texture of the mainly homeotropically aligned mesophase ripples under contractionb efore crystallization is detectable slightly above 100 8Cb yasubtle texture change without any observable flow or crystallite growth. Upon reheating, meltings ets in at 160 8C to reinstate the texture of the mesophasew ithout significant changes to the domain pattern ( Figure 5), and further heating to just below the clearingt emperature recreates ar ipple-free, mainlyn onbirefringent homeotropic texture, indicating that contrary to 7a,c rystallization in 7b proceeds without macroscopic domain reorientation and under conservation of the preformed surface alignment and column lattice orientation.…”

“…Synthesis of dibenzopentacenodithiophene-tetraester 9 and related dinaphthoperylene-tetraester 3, [3] and structure of the deriveddiimides 7 and 4 together with complementary acceptor-type perylene-diimide 5. [15] from the proton NMR spectrum,i nw hich two distinct signals exist for each of the three thiophenep rotons and for each of the three methylene or methyl positions of the outer propyl chain. These signal pairs coalescet os ingle broad featureless peaks around8 08C, and yield moderately resolved single multiplets at 120 8C.…”