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Effect of Core Twisting on Self‐Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline Phases
Author(s) -
Chen Zhijian,
Baumeister Ute,
Tschierske Carsten,
Würthner Frank
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600891
Subject(s) - perylene , columnar phase , differential scanning calorimetry , fluorescence , photoluminescence , fluorescence spectroscopy , bathochromic shift , liquid crystal , materials science , crystallography , analytical chemistry (journal) , stacking , solvatochromism , spectroscopy , chemistry , photochemistry , phase (matter) , solvent , mesophase , organic chemistry , molecule , optics , physics , optoelectronics , quantum mechanics , thermodynamics
A series of highly soluble and fluorescent core‐twisted perylene bisimide dyes (PBIs) 3 a – f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by 1 H NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The π–π aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X‐ray diffraction. Concentration‐dependent UV/Vis measurements and VPO analysis revealed that these core‐twisted π‐conjugated systems show distinct self‐dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3×10 4 and 30 M −1 . The photoluminescence spectra of the dimers of PBIs 3 a – f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective π–π stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the π systems on their π–π stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case ( 3 a ) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non‐fluorescent H ‐type into strongly fluorescent J ‐type packing of the dyes.