A rationally designed singlet sink for glassy polymeric photon upconverting films

Abstract

Photon upconverting films require high overall conversion efficiencies along with a strong absorption of incident light and a low upconversion intensity threshold (I_th) for their practical implementation (e.g. in solar harvesting, sensing, and photocatalysis). Yet, a dichotomy has emerged whereby high quantum yields seemingly come at the detriment of reasonable absorption. To date, the highest efficiency reported in 9,10-diphenylanthracene-based (DPA) amorphous films was demonstrated at low sensitizer concentrations (0.01 wt%) due to increased back-energy transfer at higher sensitizer content. The need for alternatives that circumvent this trade-off is pressing. Herein we report the rational design and application of a novel 9-phenyl-10-(p-tolylethynyl)-anthracene (PTEA) singlet sink (or collector) in conjunction with a benchmark upconverting pair, viz. platinum(II) octaethylporphyrin (PtOEP) and DPA. By using a highly fluorescent singlet exciton sink, parasitic decay to the sensitizer is circumnavigated, thus improving the upconversion quantum yield (Φ_UC) at elevated sensitizer concentrations (0.05 wt% PtOEP) compared to previous reports – expanding the potential for more practical applications for solid-state TTA-UC systems.