An N^N Platinum(II) Bis(acetylide) Complex with Naphthalimide and Pyrene Ligands: Synthesis, Photophysical Properties, and Application in Triplet–Triplet Annihilation Upconversion

Two different chromophores, pyrene (Py) and naphthalimide (NI), were introduced as acetylide ligands in a heteroleptic diimine N^N Pt II bis(acetylide) complex (Pt-NI-Py) to broaden the absorption bands and enable the intramolecular energy-transfer process. Steady-state and transient spectroscopy were used to study the photophysical properties of the complexes. The lowest triplet state of Pt-NI-Py ( τ T = 34 µs) is localized on the pyrene part, although the singlet-state energy level of the naphthalimide unit is lower. Intramolecular energy-transfer processes were observed. Moreover, Pt-NI-Py shows enhanced visible-light harvesting compared with the bis(pyrenylacetylide) complex (Pt-Py) and a lower triplet-state energy level than that of the bis(ethynylnaphthalimide) complex (Pt-NI). The results demonstrate that the relative energy levels of the singlet excited states of the different chromophores do not agree with the relative energy levels of the triplet states of the same chromophores. Efficient triplet-state generation ( Φ Δ = 0.8) gives Pt-NI-Py a high triplet–triplet annihilation (TTA) upconversion efficiency (34 %). Graphical A Pt II complex (Pt-NI-Py) with naphthalimide (NI) and pyrene (Py) chromophores as acetylide ligands exhibits a broad absorption band and pyrene-localized room-temperature phosphorescence ( Φ P = 4 %). Efficient singlet oxygen generation ( Φ Δ = 80 %) and a high quantum yield for triplet–triplet annihilation (TTA) upconversion ( Φ UC = 34 %) verify that Pt-NI-Py is a good triplet photosensitizer.