Four Slip‐Stacked Arrangements, Three Types of Photophysics: Crystal Structure and Solid‐State Fluorescence of 3,6‐Diaryl Substituted Furo[3,4‐c]furanone Polymorphs and Regioisomers

Abstract

AbstractSix symmetrical 3,6‐diaryl (aryl=phenyl, 2‐, 3‐ and 4‐tolyl, 2,4‐ and 3,5‐xylyl) substituted furo[3,4‐c]furanones (DFF) were synthesized. The computational analysis, based on density functional theory, found eight possible centrosymmetrical slipped π‐stack arrangements, formed according to electron repulsion minimization principle, as for previously reported for π‐isoelectronic diketopyrrolopyrroles (DPP). One of these slipped stack arrangements was found to form infinite columns in the crystals of a new polymorph of parent phenyl derivative (with centre‐to‐centre distance CC=6.975 Å), other three types of stacks were found for 3‐tolyl (CC=6.153 Å), 4‐tolyl (CC=3.849 Å) and 2,4‐xylyl (CC=4.856 Å) derivatives by single crystal X‐ray diffractometry. All six derivatives show intense solution fluorescence in blue/green region, with a maximum driven entirely by a number and position of methyl substituents on phenyl rings. On the other hand, the solid‐state fluorescence from yellow over orange to red is observed only for four derivatives and its presence/absence, spectral position and vibronic structure is driven exclusively by the slips in π‐stacks (with interplanar distance always less than 3.5 Å) of almost planar DFF molecules, resulting in J‐type emission, H‐type excimer‐like emission and H‐type quenching.