Abstract
Five heteroleptic Pt(II) complexes structurally defined by a diethyl-substituted bis(2-pyridylimino)isoindoline (BPI(Et)) core and an ancillary alkynyl coligand are reported. Structural variation across Pt(BPI(Et))(1-5) was achieved through different alkyne coligands: phenylacetylene (1), 4-ethynylanisole (2), 3-ethynylthiophene (3), 1-ethynyl-4-fluorobenzene (4), 1-ethynyl-4-dimethylaniline (5). Complexes were fully characterized using a range of spectroscopic and analytical techniques: (1)H and (13)C NMR, IR, UV-vis, luminescence, and transient absorption spectroscopies, HRMS, and cyclic voltammetry. Two X-ray structures revealed a subtle deviation from idealized square planar geometry where the Pt atom lies within the plane defined by the three nitrogen donors of BPI(Et). The redox behavior of the complexes showed one irreversible oxidation between +0.61 and +0.82 V (attributed to Pt(2+/3+) couple) and two well-defined ligand-based reductions with fully or quasi-reversible character between -1.70 and -2.09 V. Photophysical studies and supporting DFT calculations describe the phosphorescent nature of the complexes (λ(em) = 625-644 nm in toluene) with strong metal-to-ligand charge transfer (MLCT) character and notable singlet oxygen photogeneration (up to 73%). Triplet-triplet annihilation energy upconversion (TTA-UC) investigations in toluene indicated that this class of triplet emitting complex are viable photosensitizers with an impressive maximum efficiency of Φ(UC) = 29.6% for Pt(BPI(Et))(4).