Assembling photoactive materials from polycyclic aromatic hydrocarbons (PAHs): room temperature phosphorescence and excimer-emission in co-crystals with 1,4-diiodotetrafluorobenzene

Co-crystallization between the polycyclic aromatic hydrocarbons anthracene (A) and 9-methylanthracene (MA) with 1,4-diiodotetrafluorobenzene (I2F4) afforded three novel co-crystals, viz. A center dot(I2F4)(2) and an unexpectedly complex system with two distinct compositions, namely MA center dot I2F4 and (MA)(4)center dot I2F4, which can be mechanochemically interconverted by a change in the stoichiometry of the reactive mixtures. Interestingly, all co-crystals are dual-emissive materials and exhibit different mechanisms of emission. A center dot(I2F4)(2) and MA center dot I2F4 fluoresce from isolated molecules, whereas the luminescence of (MA)(4)center dot I2F4 is dominated by excimer emission. In all cases, phosphorescence at RT (RTP) is observed and interpreted as a direct consequence of the interactions between the iodine atoms of the I2F4 co-former and the pi-electron density of the anthracene aromatic rings. Furthermore, [4 + 4] photoactivity within (MA)(4)center dot I2F4 was also investigated by means of FTIR/NMR spectroscopy and PXRD. The photophysical and photochemical behaviors of all solids are discussed and rationalized based on their structural features.