Long‐lived Triplet Excited State of Perylenemonoimide (PMI) in a Diimine Pt(II) Bis‐acetylide Complex: Preparation and Study of the Photophysical Property with Transient Spectra

We prepared a N<^>N Pt(II) bisacetylide complex that has strong absorption of visible light (molar absorption coefficients epsilon=6.7x10(4) M-1 cm(-1) at 570 nm), and the singlet oxygen quantum yield (phi(Delta)) is up to 78 %. Femtosecond transient absorption spectra show the intersystem crossing (ISC) of the complex takes 81.8 ps, nanosecond transient absorption spectra show the triplet excited state lifetime is 7.6 mu s. Density functional theory (DFT) computation demonstrated that the S-1 and T-1 states are mainly localized on the perylenemonoimide (PMI) ligands, although the involvement of the Pt(II) centre is noticeable. The complex was used as triplet photosensitizer to generate delayed fluorescence with perylenebisimide (PBI) as the triplet state energy acceptor and emitter, via the intermolecular triplet-triplet energy transfer (TTET) and triplet-triplet annihilation (TTA), the delayed fluorescence lifetime is up to 52.5 mu s under the experimental conditions.