928342-01-2Relevant articles and documents
Effect of core twisting on self-assembly and optical properties of perylene bisimide dyes in solution and columnar liquid crystalline phases
Chen, Zhijian,Baumeister, Ute,Tschierske, Carsten,Wuerthner, Frank
, p. 450 - 465 (2007)
A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3a-f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by 1H 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 × 104 and 30 M-1. The photoluminescence spectra of the dimers of PBIs 3a-f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differ ences 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 (3a) 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.