Photon Upconversion with a Low Threshold Excitation Intensity in Plain Water

Abstract

A triplet–triplet annihilation-based photon upconversion (TTA-UC) system with a low threshold excitation intensity (I th) in plain water was developed. Water-soluble anionic porphyrin (PdTPPS4–) and diphenylanthracene (DCDPA2–) derivatives were used as light absorbers and emitter molecules, respectively, and no additives such as surfactants were required. The phosphorescence emission from PdTPPS4– under an excitation wavelength of 528 nm was quenched by DCDPA2–, resulting in triplet energy transfer, whereas fluorescence from DCDPA2– was observed in a short wavelength region (400–500 nm). Three independent emission studies utilizing different excitation light sources validated the TTA-UC process in a simple aqueous solution. TTA occurred after the triplet energy transfer, according to the time profiles of phosphorescence and fluorescence detected following pulse laser excitation. The I th for TTA-UC was estimated to be lower than 6 mW cm–2, although it could not be exactly determined due to the sensitivity limit of the experimental setup. The upper limit of I th for the aqueous solution of DCDPA2– and PdTPPS4– is the smallest value obtained to date for aqueous systems and comparable to that of high-performance TTA-UC systems in organic solutions.

Enhanced Near-Infrared-to-Visible Upconversion by a Singlet Sink Approach in a Quantum-Dot-Sensitized Triplet–Triplet Annihilation System

“…3 Its feasibility to occur under low-intensity and noncoherent radiation (e.g., sunlight) makes it more attractive to comply with photovoltaic technologies. 4 Recent advancements on NIR-to-visible UC by TTA attracted more attention to utilize the sub-band gap photons and thereby improve the power conversion efficiencies of third-generation photovoltaics beyond the Shockley− Queisser limit. 5 Normally, the TTA-UC process requires two components: a sensitizer (absorbing light) and an annihilator (or emitter, occurring TTA and emitting light), which interact via triplet−triplet energy transfer (TET).…”

“…Photon upconversion (UC) by triplet–triplet annihilation (TTA) has grown over the years, covering the different spectral ranges of UC, i.e., visible-to-ultraviolet (UV), visible-to-visible, and near-infrared (NIR)-to-visible . Its feasibility to occur under low-intensity and noncoherent radiation (e.g., sunlight) makes it more attractive to comply with photovoltaic technologies . Recent advancements on NIR-to-visible UC by TTA attracted more attention to utilize the sub-band gap photons and thereby improve the power conversion efficiencies of third-generation photovoltaics beyond the Shockley–Queisser limit .…”

Triplet quenching pathway control with molecular dyads enables the identification of a highly oxidizing annihilator class

“…Only a few annihilator structures for UC in neat water have been identified so far. 27,43–46 In addition to solubility, aggregation or excimer formation issues, one main reason for this situation is that highly polar water as the solvent favors ET over EnT reactions owing to the stabilization of (radical) ions. 43,45…”

Bulky Substituents Promote Triplet–Triplet Annihilation Over Triplet Excimer Formation in Naphthalene Derivatives

“…Triplet excimers in some TTA-UC systems have been suggested but not verified previously, , but are herein spectrally observed by means of nanosecond transient absorption. These findings are important for the continued search for high-performing annihilator compounds, as many chromophores for TTA-UC are based on anthracene, − naphthalene, ,,, or benzene, all of which are known to form triplet excimers. − …”