Examining the role of acceptor molecule structure in self-assembled bilayers: surface loading, stability, energy transfer, and upconverted emission

Abstract

Self-assembly of sensitizer and acceptor molecules has recently emerged as a promising strategy to facilitate and harness photon upconversion via triplet-triplet annihilation (TTA-UC). In addition to the energetic requirements, the structure and relative orientation of these molecules can have a strong influence on TTA-UC rates and efficiency. Here we report the synthesis of five different acceptor molecules composed of an anthracene core functionalized with 9,10- or 2,6-phenyl, methyl, or directly bound phosphonic acid groups and their incorporation into self-assembled bilayers on a ZrO2 surface. All five films facilitate green-to-blue photon upconversion with Φuc as high as 0.0023. The efficiency of TTA, and not triplet energy transfer, fluorescence, or losses via FRET, was primarily responsible for dictating the Φuc emission. Even for molecules having similar photophysical properties, variation in the position of the phosphonic acid resulted in dramatically different ΦTTA, Ith values, γTTA, and D. Interestingly, we observed a strong linear correlation between ΦTTA and the Ith value but the cause of this relationship, if any, is unclear.

On the Quantum Yield of Photon Upconversion via Triplet–Triplet Annihilation

“…In addition to Φ UC we have defined the quantum yield of photons generated (Φ UCg ) with the difference being the output coupling yield (Φ out ). 21 The reason for this distinction is that Φ UC is not necessarily intrinsic to the TTA-UC system but instead dependent on the sample architecture and the method of measurement (i.e., relative vs absolute). Output losses include waveguiding, scattering, inner filtering effects, etc.…”

Singlet Sensitization-Enhanced Upconversion Solar Cells via Self-Assembled Trilayers

“…While there are several strategies for harnessing sunlight using TTA-UC, − metal ion linked, multilayer assemblies of acceptor (aka, annihilator) ( A ) and triplet sensitizer ( S ) molecules on TiO 2 (Figure ) have emerged as one of the most promising approaches for directly integrating TTA-UC into a solar cell. − The layered structure enables directional energy transfer, the molecular proximity is favorable for energy migration and TTA, , and the metal oxide surface can extract charge from the UC state resulting in TTA-UC photocurrent density of up to 0.158 mA cm –2 under 1 sun (AM1.5) . This photocurrent density enhancement is above the device relevant threshold of 0.1 mA cm –2 , but given previously reported TTA-UC efficiencies, >1 mA cm –2 is most certainly attainable and could increase device efficiency records for DSSCs or perovskite solar cells by one percentage point or more .…”

A Sustainable Improvement of ω-Bromoalkylphosphonates Synthesis to Access Novel KuQuinones

“…Acid hydrolysis was then performed with 0.5 M of hydrochloric acid, under microwave irradiation, with no results, likely because of the poor KuQuinone solubility in water [55]. Additionally, hydrolysis with bromotrimethylsilane (TMSBr) [56][57][58] was not successful. At this point, considering a seminal work by Morita [59], KuQuinone phosphonate ester hydrolysis has been performed with TMSBr in the presence of NaI (Table 3).…”