The Butterfly Effect in Bisfluorenylidene-based Dihydroacenes: Aggregation Induced Emission and Spin Switching

Linear acenes are a well-studied class of polycyclic aromatic hydrocarbons and their established physical properties has led to their widespread application across the field of organic electronics. However, their quinoidal forms – the dihydroacenes – are much less explored and exhibit vastly different photophysical and electronic properties due to their non-planar, cross-conjugated nature. In this work, we present a series of difluorenylidene dihydroacenes which exhibit a butterfly-like structure with a quinoidal skeleton, resulting in comparatively higher optical band gaps and lower redox activities to their planar analogs. We found these compounds exhibit aggregation induced emission (AIE), activated through restriction of the “flapping” vibrational mode of the molecules in the solid state. Furthermore, anthracene-containing dihydroacenes exhibited thermally activated ground-state spin switching as evidenced by planarization of the acene core and diradical activity recorded by EPR. These two characteristics in this relatively unexplored class of materials provides new insights for the design of multifunctional materials.