Room-Temperature Phosphorescence of Cocrystals of Aromatic Bisimides and Triplet Sensitizer Pt(acac)2

Additional data to report https://doi.org/10.1002/adfm.202412843:

Four sterically shielded aromatic bisimides are synthesized and their ability to form cocrystals with the triplet sensitizer platinum(II) acetylacetonate (Pt(acac)2) is investigated. Single crystals of the individual electron-deficient bisimides are studied first, two showing bright blue fluorescence with quantum yields up to 28%, while the other two barely emit at all. After successful cocrystallization of all four aromatic bisimides with the electron-rich Pt(II) complex, two different stoichiometries, either 1:1 or 1:2, are found in the crystalline solid state, whose absorbance and photoluminescence exhibit distinct bathochromic shifts. While two naphthalene bisimides show strong and long-lived room-temperature phosphorescence (RTP) with quantum yield up to over 50%, the other two aromatic bisimides show only minor photoluminescence at RT, but a bright low-temperature phosphorescence (LTP) at 80 K. Theoretical calculations reveal the importance of changing the magnetic quantum number m of the involved d-orbitals at the platinum center as well as the alignment of the Pt(II) center above an aromatic C-C bond for an efficient intersystem crossing in these systems.