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Design and Synthesis of Bipyridine Platinum(II) Bisalkynyl Fullerene Donor–Chromophore–Acceptor Triads with Ultrafast Charge Separation

Lee, Sai-Ho, Chan, Chris Tsz-Leung, Wong, Keith Man-Chung, Lam, Wai Han, Kwok, Wai-Ming, Yam, Vivian Wing-Wah
Journal of the American Chemical Society 2014 v.136 no.28 pp. 10041-10052
absorption, electrochemistry, electron transfer, energy transfer, fullerene, methylene chloride, models, platinum, spectroscopy
Donor–chromophore–acceptor triads, (PTZ)₂-Pt(bpy)-C₆₀ and (ᵗBuPTZ)₂-Pt(bpy)-C₆₀, along with their model compound, (Ph)₂-Pt(bpy)-C₆₀, have been synthesized and characterized; their photophysical and electrochemical properties have been studied, and the origin of the absorption and emission properties has been supported by computational studies. The photoinduced electron transfer reactions have been investigated using the femtosecond and nanosecond transient absorption spectroscopy. In dichloromethane, (Ph)₂-Pt(bpy)-C₆₀ shows ultrafast triplet–triplet energy transfer from the ³MLCT/LLCT excited state within 4 ps to give the ³C₆₀* state, while in (PTZ)₂-Pt(bpy)-C₆₀ and (ᵗBuPTZ)₂-Pt(bpy)-C₆₀, charge-separated state forms within 400 fs from the ³MLCT/LLCT excited state with efficiency of over 0.90, and the total efficiency with the contribution of ³C₆₀* is estimated to be 0.99. Although the forward electron transfer reactions are very rapid, the charge-separated state recombines to the singlet ground state at a time of hundreds of nanoseconds because of the difference in spin multiplicity between the charge-separated state and the ground state.