Polymorph of dimethylacetamide-solvated crystals of 2,9-dichlorodithioketoquinacridone and their hydrogen bonding effect

摘要

2,9-Dichlorodithioketoquinacridone (DTQ-Cl) is a thionated derivative of industrially important 2,9-dichloroquinacridone used as colorants in painting and imaging industries.Crystallographic and electronic characterizations have been carried out on single crystals of DTQ-Cl recrystallized from solution in dimethylacetamide (DMA).Two kinds of DMA-solvated single crystals were isolated in the form of DTQ-Cl/(DMA)_2: modifications I and II.In both crystals,two DMA molecules are hydrogen-bonded to one DTQ-Cl molecule.Modifications I and II crystallize in different space groups: P2_1/c and P1,respectively.The DTQ-Cl molecules are arranged in a fashion "hunter's fence" in modification I;whereas all DTQ-Cl molecules are nearly on the molecular plane and stacked in a layered structure in modification II.MO calculations based on the X-ray coordinates revealed that the absorption bands for both DTQ-Cl and DTQ-C1/(DMA)_2 are expected to appear at longer wavelengths in modification I than in modification II.However,the reverse is the case in experiment.This can be attributed to the difference in excitonic interactions along the stacking axis in modifications I and II.