Room-Temperature High-Efficiency Solid-State Triplet–Triplet Annihilation Up-Conversion in Amorphous Poly(olefin sulfone)s

• Published in: ACS applied materials & interfaces 2017-03, Vol.9 (9), p.8280-8286
• Main Authors: Turshatov, Andrey, Busko, Dmitry, Kiseleva, Natalia, Grage, Stephan. L, Howard, Ian A, Richards, Bryce S
• Format: Article
• Language: English
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.6b12625

Triplet–triplet annihilation up-conversion (TTA-UC) is a developing technology that can enable spectral conversion under sunlight. Previously, it was found that efficient TTA-UC can be realized in polymer hosts for temperatures above the polymer’s glass transition (T > T g). In contrast, TTA-UC with high quantum yield for temperatures below T g is rarely reported. In this article, we report new polymer hosts in which efficient TTA-UC is observed well below T g, when the polymer is in a fully solid state. The four poly­(olefin sulfone) hosts were loaded with upconversion dyes, and absolute quantum yields of TTA-UC (ηTTA‑UC) were measured. The highest value of ηTTA‑UC = 2.1% was measured for poly­(1-dodecene sulfone). Importantly, this value was the same in vacuum and at ambient conditions, indicating that the host material acts as a good oxygen barrier. We performed time-resolved luminescence experiments in order to elucidate the impact of elementary steps of TTA-UC. In addition to optical characterization, we used magic angle spinning solid-state NMR experiments to estimate the T2 transverse relaxation time. Relatively long T2 times measured for poly­(olefin sulfone)­s indicate an enhanced nanoscale fluidity in the studied (co)­polymers, which unexpectedly coexists with a rigidity on the macroscale. This would explain the exceptional triplet energy transfer between the guest molecules, despite the macroscopic rigidity.