Triplet–Triplet Annihilation Upconversion by Polymeric Sensitizers

Abstract

Triplet-triplet annihilation up-conversion (TTAUC) is an emerging technology in photonics with significant potential to impact a variety of fields (e.g. solar cells, bioimaging, drug delivery) due to its ability to convert long-wavelength photons to higher photon energies even at low excitation power densities. However, for many practical applications of TTAUC, the transfer of the upconversion system, consisting of a molecular sensitizer and a molecular annihilator, from solution, in which efficient TTAUC systems have been reported, to solid matrices is required. This is a challenge because diffusion facilitates the close contact between molecular components required for TTET and TTA. To this end, various approaches to fully integrate sensitizer and annihilator into polymers or combining a macromolecular annihilator with monomeric sensitizers have been established. This contribution studies the effect of integrating Ru(dqp)2-inspired molecular sensitizers into the side chains of a PMMA polymer, whichas macromolecular photosensitizeris co-dissolved with 9,10-diphenylanthracene as annihilator. We study the effect of confining the sensitizers into a comparably small volume on the TTAUC process and compare the results to an upconversion system using various concentrations of monomeric annihilator. We show that our approach of using a macromolecular photosensitizer allows for upconversion at extremely low excitation power densities. Furthermore, the onset of the strong annihilation regime, i.e. the regime in which the intensity of the upconverted light scales linearly with the increase of the excitation power, is significantly reduced using the polymeric sensitizer; however, the upconversion intensity sits below the monomeric counterparts.

Ultrafast Infrared-to-Visible Photon Upconversion on Plasmon/TiO2 Solid Films

“…Hence, triplet–triplet annihilation upconversion process systems require substantial optimization to transfer successful concepts functioning well in solution to materials. Some systems have been realized in a solid state/gel environment and fully polymer-integrated systems, − but the quantum yield remains low compared to the liquid systems. Moreover, few polymers or gels have suitable compatibility, stability, and optical inertness.…”

Progress and perspectives: fluorescent to long-lived emissive multifunctional probes for intracellular sensing and imaging

“…158 The TTA process in such a probe involves the triplet state of an organic molecule as an intermediate excited state. 201,202 Generally, the probe consists of molecules known as a sensitizer and an annihilator having similar triplet energies. The sensitizer absorbs the energy and transfers its triplet energy to the annihilator resulting in a triplet excited state of the annihilator.…”

BODIPY‐Perylene Charge Transfer Compounds; Sensitizers for Triplet‐Triplet Annihilation Up‐conversion

“…TTA-UC typically has a low excitation threshold without the requirement for coherent visible and near-infrared (NIR) light sources, and this is a significant advantage over other types of up-conversion. [5,6] In contrast to classical luminescence, where the emission is Stokes shifted, TTA-UC yields an anti-Stokes shifted emission via the process summarized in Scheme 1. In TTA-UC a sensitizer molecule (S) is excited to its first singlet state, by a longwavelength photon.…”

“…One sub‐type of up‐conversion that is attracting increasing interest is triplet‐triplet annihilation up‐conversion (TTA‐UC). TTA‐UC typically has a low excitation threshold without the requirement for coherent visible and near‐infrared (NIR) light sources, and this is a significant advantage over other types of up‐conversion [5,6] …”