Effect of Core Twisting on Self-Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline Phases

摘要

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 pi-pi 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 pi-con-jugated systems show distinct self-di-merization equilibria in apolar solvent methylcyclohexane(MCH)with dime-rization constants between 1.3 X 10~4 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 differences in the respective PI-PI stacking distance.In condensed state,quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low iso-tropization temperatures.The effects of the distortion of the pi systems on their pi-pi 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 pi-type into strongly fluorescent J-type packing of the dyes.