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

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 (η TTA-UC ) were measured. The highest value of η TTA-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.