Loss channels in triplet-triplet annihilation photon upconversion: importance of annihilator singlet and triplet surface shapes
Journal article, 2017

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).

Author

Victor Gray

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Polymer Technology

Ambra Dreos

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Polymer Technology

Paul Erhart

Chalmers, Physics, Materials and Surface Theory

Bo Albinsson

Chalmers, Chemistry and Chemical Engineering, Chemistry and Biochemistry, Physical Chemistry

Kasper Moth-Poulsen

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Polymer Technology

Maria Abrahamsson

Chalmers, Chemistry and Chemical Engineering, Chemistry and Biochemistry, Physical Chemistry

Physical Chemistry Chemical Physics

1463-9076 (ISSN) 1463-9084 (eISSN)

Vol. 19 17 10931-10939

Subject Categories

Atom and Molecular Physics and Optics

DOI

10.1039/c7cp01368j

More information

Latest update

5/17/2018