Synthesis and X-ray crystallography of bipyrroles: impacts of a CO-π interaction on their structure

Crystal structures and solid-state emission properties of tetraalkyl 4,4'-dimethyl-2,2'-bipyrrole-3,3',5, 5'-tetracarboxylates (alkyl = methyl, ethyl, and isopropyl) have been investigated. Single crystal X-ray diffraction studies revealed that all bipyrroles are co-planar due to an intramolecular hydrogen bonding. The isopropyl derivative exhibited a C=O center dot center dot center dot pi interaction in the solid-state and showed the longest emission wavelength because of increase in structural flexibility. (C) 2015 Elsevier Ltd. All rights reserved.