| Keywords [eng] |
triplet-triplet annihilation, photon upconversion, 9,10-dialkynylanthracene, annihilator, Sonogashira cross-coupling, spin-statistical factor, fluorescence quantum yield, anti-Stokes emission |
| Abstract [eng] |
A series of seven 9,10-diethynylanthracene derivatives bearing triethylsilyl (11), triisopropylsilyl (12), triphenylsilyl (15), triphenylmethyl (14), triethylgermyl (20), TIPS-diynyl (13), and n-hexyl (10) substituents was synthesized in 52–92% yield by Sonogashira cross-coupling and lithium acetylide addition, and evaluated as annihilators for triplet–triplet annihilation upconversion (TTA-UC) with PtOEP as sensitizer. Triplet sensitization was quantitative across the series (φISC = 100%, φTET ≥ 98%), placing all performance differences in the annihilator domain. The trityl compound 14 gave φ~UC~ = 25.5% (f = 80.9%) — the highest in the series and on par with the benchmark DPA — attributed to the unique combination of steric protection and the absence of electronic conjugation at the sp³-trityl center. A decrease in φFL and φUC observed for the Ge-containing compound 20 relative to its Si analogue 12 is consistent with stronger spin-orbit coupling at the heavier center promoting non-radiative decay, though this interpretation remains a hypothesis pending further investigation. Extension of the alkyne spacer or ring fusion of the anthracene core suppressed upconversion in both cases, consistent with T1 energy mismatch with the PtOEP sensitizer. Microwave-assisted Sonogashira coupling reduced reaction times ten-fold and enabled chromatography-free isolation in several cases. Attempts to access tin-containing and adamantyl-substituted derivatives were unsuccessful — attributed tentatively to product protodestannylation and bridgehead inaccessibility, respectively — and remain targets for future work. |
