No abstract

Photon upconversion via triplet–triplet annihilation (TTA) has promise for overcoming the Shockley–Queisser limit for single‐junction solar cells by allowing the utilization of sub‐bandgap photons. Recently, bulk perovskites have been employed as sensitizers in solid‐state upconversion devices to circumvent poor exciton diffusion in previous nanocrystal (NC)‐sensitized devices. However, an in‐depth understanding of the underlying photophysics of perovskite‐sensitized triplet generation is still lacking due to the difficulty of precisely controlling interfacial properties of fully solution‐processed devices. In this study, interfacial properties of upconversion devices are adjusted by a mild surface solvent treatment, specifically altering perovskite surface properties without perturbing the bulk perovskite. Thermal evaporation of the annihilator precludes further solvent contamination. Counterintuitively, devices with more interfacial traps show brighter upconversion. Approximately an order of magnitude difference in upconversion brightness is observed across different interfacial solvent treatments. Sequential charge transfer and interfacial trap‐assisted triplet sensitization are demonstrated by comparing upconversion performance, transient photoluminescence dynamics, and magnetic field dependence of the devices. Incomplete triplet conversion from transferred charges and consequent triplet‐charge annihilation (TCA) are also observed. The observations highlight the importance of interfacial control and provide guidance for further design and optimization of upconversion devices using perovskites or other semiconductors as sensitizers.

Molecules that undergo reverse intersystem-crossing (RISC), which enables thermally activated delayed fluorescence, represent an important advance in the development of organic-based light-emitting diodes (OLEDs). The current study focuses on two blue-emitting RISC molecules employing carbazole as the donor and benzothiazole or benzoxazole derivative as the acceptor (BTZ/BOX-carbazole (CBZ)). Although the emission maxima of these compounds are deep blue (∼410 nm) in hydrocarbon solvents, their spectra broaden, red shift, and decrease in intensity with even a modest increase in solvent polarity because of their strong charge-transfer (CT) character. These effects are qualitatively predicted from time-dependent density functional theory calculations using the state-specific polarizable continuum model, though the emission spectral shifts are significantly overestimated. The desired blue emission peak of both compounds (∼425 nm) is recovered by rigidifying the environment, either in low-temperature glasses or in room-temperature polymer films, independent of local polarity. The polarity-induced emission red shift is therefore due to the solvent orientational polarizability. The effects of an applied electric field on the spectra (Stark effect) are used to quantify the CT character of the absorbing and emitting states. Significantly less field-induced emission quenching is observed in BOX-CBZ versus that in BTZ-CBZ. Minimizing this effect is important for the performance in the large (1–10 MV) fields present within OLED devices.

Strychnine-sensitive glycine receptors (GlyR) play a major role in the excitability of CNS neurons and are also a major target of many drugs including some general anesthetics and ethanol. The prefrontal cortex (PFC) is an important substrate responsible for cognitive function and for sedation, as well as hypnosis (unconsciousness) which is induced by general anesthetics and ethanol. However, the functions and the physiological and pharmacological properties of GlyRs in mature PFC neurons have not been well studied. In this study, whole-cell currents induced by glycine (IGly) were recorded from freshly isolated PFC neurons of Sprague-Dawley rats aged 5 to 39 postnatal days (neonatal, P5–12; weanling, P17–21 and peri-adolescent, P30–39). We found that most of the neurons examined were responsive to glycine and the response was concentration dependent. With the increase of age, the sensitivity to glycine was significantly decreased and the sensitivity to picrotoxin was significantly increased. Conversely, the changes in sensitivity to strychnine were not significant. Interestingly, IGly of all age groups was suppressed (to different scope) by low concentrations of picrotoxin (≤ 30 µM), which selectively blocked α homomeric GlyRs. Conversely, about 20–65% of IGly remained in the presence of 300 µM picrotoxin, suggesting the picrotoxin-resistant subtype the αβ heteromeric GlyR, was also present. These data provide the first evidence that there are at least two subtypes of functional GlyRs in the PFC neurons of young rats, and their physiological and pharmacological properties change substantially during maturation.

Mechanistic studies of the morphology of lead halide perovskite nanocrystals (LHP‐NCs) are hampered by a lack of generalizable suitable synthetic strategies and ligand systems. Here, the synthesis of zwitterionic CsPbBr3 NCs is presented with controlled anisotropy using a proposed “surface‐selective ligand pairs” strategy. Such a strategy provides a platform to systematically study the binding affinity of capping ligand pairs and the resulting LHP morphologies. By using zwitterionic ligands (ZwL) with varying structures, majority ZwL‐capped LHP NCs with controlled morphology are obtained, including anisotropic nanoplatelets and nanorods, for the first time. Combining experiments with density functional theory calculations, factors that govern the ligand binding on the different surface facets of LHP‐NCs are revealed, including the steric bulkiness of the ligand, the number of binding sites, and the charge distance between binding moieties. This study provides guidance for the further exploration of anisotropic LHP‐NCs.