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The structures of the red polymorph (space group P1) and the black polymorph (space group P21/c) of 4,4′‐dimethyl‐6,6′‐dichlorothioindigo were solved from single‐crystal samples. For both polymorphs, the spatial stacking of the flat molecules is driven by π‐stacking and noncovalent interactions within the layers. Spectroscopic (UV–vis, IR and photoluminescence) and thermal properties of the red polymorph were investigated experimentally. The bandgap of this polymorph was estimated as 2.08 eV at room temperature. It is demonstrated that the electric conductivity of the red polymorph follows the hopping mechanism. [ABSTRACT FROM AUTHOR]

The crystal structures of two polymorphs of cis‐perinone (bisbenzimidazo[2,1‐b:1′,2′‐j]benzo[lmn][3,8]phenanthroline‐6,9‐dione, Pigment Red 194) were solved from single crystals obtained solvothermally from 1,2‐dichlorobenzene or n‐butanol at 220°C. Both crystal structures (space group P21/c) derive from stacking of flat molecules arranged due to π–π interaction. The melting points of these two polymorphs are 471°C and 468°C and their respective optical bandgaps are 1.94 eV and 1.71 eV. One of the polymorphs demonstrates drift and hopping mechanisms of electric conductivity, whereas the other one is dominated by the drift conductivity. The direct current (DC) electric conductivity of the samples are 4.77 × 10−13 S m−1 and 6.84 × 10−10 S m−1 at room temperature. The significant difference in DC conductivities can be explained by the dependence of the mobility and concentration of charge carriers on the structure of the samples. [ABSTRACT FROM AUTHOR]