Photo-induced electron transfer in a diamino-substituted Ru(bpy)3[PF6]2 complex and its application as a triplet photosensitizer for nitric oxide (NO)-activated triplet—triplet annihilation upconversion

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Abstract
A system demonstrating Nitric Oxide (NO) activated Triplet–Triplet Annihilation (TTA) upconversion has been devised, based on a substituted [RuII(bpy)3](PF6)2 complex (bpy = 2,2′-dipyridine) bearing a single 1,2-diaminophenyl moiety as an NO activatable triplet photosensitizer (Ru-1), and 9,10-diphenylanthracene (DPA) as a triplet acceptor/emitter. The excited triplet state of Ru-1 is significantly quenched (ΦT ∼ 22%) by a Photoinduced Electron Transfer (PET) reaction, as confirmed by steady state phosphorescence and transient absorption spectroscopy, and hence Ru-1 does not function as a TTA upconversion sensitizer. However, in the presence of NO/O2, the 1,2-diaminophenyl group of Ru-1 is transformed into a benzotriazole. This inhibits PET, and the triplet state quantum yield is increased to ca. 85%, switching on the TTA upconversion process which increases by 10-fold. These processes were studied using a combination of steady state and time-resolved luminescence together with transient absorption spectroscopy on the nanosecond and femtosecond timescales. The energy level of the charge transfer state (CTS) for Ru-1 was also obtained electrochemically, supporting the PET mechanism of triplet state quenching and hence the lack of TTA upconversion with Ru-1.
Funding Information
  • Royal Society (21011130154)
  • Dalian University of Technology (DUT14ZD226, DUT2013TB07)
  • University of Queensland (MEI-2013000106)
  • Ministry of Education (IRT_13R06, SRFDP-20120041130005)
  • Australian Research Council (FT100100795)

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