Long-Lived Room-Temperature Near-IR Phosphorescence of BODIPY in a Visible-Light-Harvesting N C N PtII-Acetylide Complex with a Directly Metalated BODIPY Chromophore

Room-temperature long-lived near-IR phosphorescence of boron-dipyrromethene (BODIPY) was observed (lambda em=770 nm, Phi(P)=3.5%, tau P=128.4 mu s). Our molecular-design strategy is to attach PtII coordination centers directly onto the BODIPY p-core using acetylide bonds, rather than on the periphery of the BODIPY core, thus maximizing the heavy-atom effect of Pt-II. In this case, the intersystem crossing (ISC) is facilitated and the radiative decay of the T1 excited state of BODIPY is observed, that is, the phosphorescence of BODIPY. The complex shows strong absorption in the visible range (e=53800M(-1)cm(-1) at 574 nm), which is rare for Pt-II-acetylide complexes. The complex is dual emissive with 3MLCT emission at 660 nm and the 3IL emission at 770 nm. The T1 excited state of the complex is mainly localized on the BODIPY moiety (i.e. 3IL state, as determined by steady-state and time-resolved spectroscopy, 77 K emission spectra, and spin-density analysis). The strong visible-light-harvesting ability and long-lived T1 excite state of the complex were used for triplet-triplet annihilation based upconversion and an upconversion quantum yield of 5.2?% was observed. The overall upconversion capability (eta=epsilon x Phi(UC)) of this complex is remarkable considering its strong absorption. The model complex, without the BODIPY moiety, gives no upconversion under the same experimental conditions. Our work paves the way for access to transition-metal complexes that show strong absorption of visible light and long-lived 3IL excited states, which are important for applications in photovoltaics, photocatalysis, and upconversions, etc.