Swallow-Tail Substituted Liquid Crystalline Perylene Bisimides: Synthesis and Thermotropic Properties

Abstract

Tailor-made synthesis and structure-property relationship of several swallow-tail N-substituted perylene bisimide (PBI) dyes are presented. PBI derivatives were synthesized by two distinct synthetic approaches, the details being evaluated herein. All the PBIs carry either alkyl swallow-tail or oligoethylenglycolether (OEG) swallow-tail moieties as N-substituents, and many of them are unsymmetrically substituted. We avoided substitution at bay positions of the perylene core to maintain the planarity and strong pi-pi interactions, which favor intermolecular order and charge carrier transport. The thermotropic behavior, which is strongly influenced by the nature of the substituents was investigated using differential scanning calorimetry (DSC), polarization optical microscopy (POM), and X-ray diffraction measurements (XRD). The introduction of OEG swallow-tail units facilitates thermotropic liquid crystalline behavior in most cases and the unsymmetrical substitution allowed the tuning of the mesophase-width. The mesophases exhibit characteristic columnar hexagonal (Col(h)) packing arising from pi-pi interactions between cofacially orientated perylene molecules. Thus, the inherent tendency of PBI molecules for crystallization could be effectively suppressed by incorporating flexible OEG swallow-tail units only at imide positions. This molecular design was crucial to obtain liquid crystallinity and intracolumnar long-range order. The substituents did not influence the electronic energy levels such as HOMO and LUMO.

N‐Type Self‐Assembled Monolayer Field‐Effect Transistors and Complementary Inverters

“…The LUMO of the PBI-PA is estimated at around 3.8 eV. [ 26 ] Despite the injection barrier of more than 1 eV, electrons can still be injected. Comparable contact limited injection has been reported for thin-fi lm transistors of semiconducting PBI derivatives.…”

Mesoporous Organosilica Hybrids Consisting of Silica‐Wrapped π–π Stacking Columns

“…However, all of the conventional crystallike PMOs show lamellar structures consisting of alternating organic and silica layers (Figure 1 a, left). [13][14][15][16][17][18][19][20] In this configuration, the distance between neighboring organic bridges is about 0.44 nm, which is much longer than typical face-to-face p-p stacking distances (0.34-0.36 nm); [21,22] therefore, neither strong electronic coupling nor significant electroconductive properties are expected for the pore walls. The lamellar arrangement is thought to be directed by a hydrophobichydrophilic interaction of fully hydrolyzed dipodal precursors ((HO) 3 SiÀRÀSi(OH) 3 ) and subsequent polycondensation; the position and distance of the organic bridges are restricted by the chemical bond length of the siloxane network.…”

Singular Temperatures Connected to Charge Transport Mechanism Transitions in Perylene Bisimides from Steady-State Photocurrent Measurements

“…Its structure is characteristic for discotic packing in which the PBI building blocks assemble into columns arranged in a hexagonal unit cell. 9,19,20 6 illuminate the samples. Since absorption is low and the light distribution inside the material is quite uniform, the conductivity and photoconductivity values can be calculated without using correction factors.…”