Möhlau’s Anthradipyrazole Revisited: A New Look at an Old Molecular System

Two polymorphs of 2,7-dihydrobenzo­[1,2,3-cd:4,5,6-c′d′]­diindazole (“dipyrazoloanthracene”; α and β; DBDI) were isolated and fully characterized by means of structural X-ray powder diffraction methods, thermal, and extended spectroscopic analyses. Different interconversion paths between the two species were evidenced. UV–vis absorption, emission, and excitation spectra were measured, while time-resolved fluorescence studies allowed for the detection of multiple decay processes. In the two species, NH···N hydrogen bonds give rise to manifestly different structures, which, in the rhombohedral β phase, generate permanent porosity. This feature has been further characterized by CO₂/N₂/CH₄ sorption isotherms at different temperatures, highlighting a significant selectivity favoring CO₂ trapping.