Synergetic effect of coordination and the arylacetylide ligands on the photophysical properties of cyclometalated platinum complexes

Six coordinated Pt(II) complexes were prepared, in which the C*N<^>N or the C<^>N<^>N ligand were used to form the Pt(II) coordination center. For each coordination profile, three different arylacetylide ligands were used, i.e. naphthalenediimide (NDI), pyrenyl (Py) and naphthaleneimide (NI) acetylides. The electrochemical and the photophysical properties of the complexes were studied with steady-state and time-resolved absorption and emission spectroscopy, cyclic voltammetry and DFT calculations. The photostability and the photoluminescent properties of the complexes are finely tuned by the photoredox and photophysical properties of the arylacetylide ligands and the C*N<^>N/C<^>N<^>N Pt(II) coordination center. The triplet excited states of the complexes are an intraligand feature and the lifetime is long (90.1 mu s). The photophysical properties of the complexes were rationalized with DFT calculations. The complexes were used as triplet photosensitizer for triplet-triplet annihilation upconversion. The upconversion quantum yield was up to 29.7%. The results are useful for future designing of Pt(II) complexes showing strong visible light-absorption, RT phosphorescence and long-lived triplet excited states.