Cationic Iridium Complexes with Intramolecular π–π Interaction and Enhanced Steric Hindrance for Solid-State Light-Emitting Electrochemical Cells

Cationic iridium complexes incorporated 4,5-diaza-9,9′-spirobifluorene as N∧N ancillary ligands, in which one (2) or two (3) phenyl groups were introduced onto 4,5-diazafluorene to afford intraligand π–π interactions. The X-ray crystal structures of complexes 2 and 3 show that the pendant phenyl ring forms strong intramolecular face-to-face π-stacking with the difluorophenyl ring of the cyclometalated ligand with distances of 3.38 Å for complex 2 and 3.40 and 3.46 Å for complex 3. This π–π stacking interaction minimizes the expansion of the metal–ligand bonds in the excited state, resulting in a longer device lifetime in the light-emitting electrochemical cell (LEC) devices.以4,5-二氮杂-9,9′-螺二芴作为N∧N型辅助配体的阳离子铱配合物，在其4,5-二氮杂芴结构单元上分别引入1个（配合物2）或2个（配合物3）苯基，以构建配体内π-π相互作用。配合物2与3的X射线晶体结构显示，其悬挂苯基环与环金属化配体的二氟苯基环形成强分子内面对面π堆积：配合物2的堆积距离为3.38 Å，配合物3的两处堆积距离分别为3.40 Å与3.46 Å。该π-π堆积相互作用可抑制激发态下金属-配体键的膨胀，进而延长发光电化学电池（LEC）器件的使用寿命。