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

<p>Additional data to report <a href="https://doi.org/10.1002/adfm.202412843">https://doi.org/10.1002/adfm.202412843</a>:</p> <p>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 <em>m</em> of the involved <em>d</em>-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.</p>