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

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: P21/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-Cl/(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.