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Loss channels in triplet-triplet annihilation photon upconversion: importance of annihilator singlet and triplet surface shapes

Victor Gray (Institutionen för kemi och kemiteknik, Polymerteknologi) ; Ambra Dreos (Institutionen för kemi och kemiteknik, Polymerteknologi) ; Paul Erhart (Institutionen för fysik, Material- och ytteori (Chalmers)) ; Bo Albinsson (Institutionen för kemi och kemiteknik, Fysikalisk kemi) ; Kasper Moth-Poulsen (Institutionen för kemi och kemiteknik, Polymerteknologi) ; Maria Abrahamsson (Institutionen för kemi och kemiteknik, Fysikalisk kemi)
Physical Chemistry Chemical Physics - PCCP (1463-9076). Vol. 19 (2017), 17, p. 10931-10939.
[Artikel, refereegranskad vetenskaplig]

Triplet-triplet annihilation photon upconversion (TTA-UC) can, through a number of energy transfer processes, efficiently combine two low frequency photons into one photon of higher frequency. TTA-UC systems consist of one absorbing species (the sensitizer) and one emitting species (the annihilator). Herein, we show that the structurally similar annihilators, 9,10-diphenylanthracene (DPA, 1), 9-(4-phenylethynyl)10-phenylanthracene (2) and 9,10-bis(phenylethynyl) anthracene (BPEA, 3) have very different upconversion efficiencies, 15.2 +/- 2.8%, 15.9 +/- 1.3% and 1.6 +/- 0.8%, respectively (of a maximum of 50%). We show that these results can be understood in terms of a loss channel, previously unaccounted for, originating from the difference between the BPEA singlet and triplet surface shapes. The difference between the two surfaces results in a fraction of the triplet state population having geometries not energetically capable of forming the first singlet excited state. This is supported by TD-DFT calculations of the annihilator excited state surfaces as a function of phenyl group rotation. We thereby highlight that the commonly used "spin-statistical factor'' should be used with caution when explaining TTA-efficiencies. Furthermore, we show that the precious metal free zinc octaethylporphyrin (ZnOEP) can be used for efficient sensitization and that the upconversion quantum yield is maximized when sensitizer-annihilator spectral overlap is minimized (ZnOEP with 2).

Denna post skapades 2017-07-06. Senast ändrad 2017-11-20.
CPL Pubid: 250552


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