JPCL : One Year In Scholes, Gregory D
The journal of physical chemistry letters,
2021-Jan-14, 2021-01-14, 20210114, Letnik:
12, Številka:
1
Journal Article
Charge carrier trapping is an important phenomenon in nanocrystal (NC) decay dynamics because it reduces photoluminescence (PL) quantum efficiencies and obscures efforts to understand the interaction ...of NC excitons with their surroundings. Particularly crucial to our understanding of excitation dynamics in, e.g., multiNC assemblies, would be a way of differentiating between processes involving trap states and those that do not. Direct optical measurement of NC trap state processes is not usually possible because they have negligible transition dipole moments; however, they are known to indirectly affect exciton photoluminescence. Here, we develop a framework, based on Marcus electron transfer theory, to determine NC trap state dynamics from time-resolved NC exciton PL measurements. Our results demonstrate the sensitivity of PL to interfacial dynamics, indicating that the technique can be used as an indirect but effective probe of trap distribution changes. We anticipate that this study represents a step toward understanding how excitons in nanocrystals interact with their surroundings: a quality that must be optimized for their efficient application in photovoltaics, photodetectors, or chemical sensors.
The development of elegant synthetic methodologies for the preparation of monocomponent nanocrystalline particles has opened many possibilities for the preparation of heterostructured semiconductor ...nanostructures. Each of the integrated nanodomains is characterized by its individual physical properties, surface chemistry, and morphology, yet, these multicomponent hybrid particles present ideal systems for the investigation of the synergetic properties that arise from the material combination in a non‐additive fashion. Of particular interest are type‐II heterostructures, where the relative band alignment of their constituent semiconductor materials promotes a spatial separation of the electron and hole following photoexcitation, a highly desirable property for photovoltaic applications. This article highlights recent progress in both synthetic strategies, which allow for material and architectural modulation of novel nanoheterostructures, as well as the experimental work that provides insight into the photophysical properties of type‐II heterostructures. The effects of external factors, such as electric fields, temperature, and solvent are explored in conjunction with exciton and multiexciton dynamics and charge transfer processes typical for type‐II semiconductor heterostructures.
The characteristic band alignment of the constituent semiconductor materials in type‐II heterostructures promotes spatial separation of the photoexcited carriers. The photophysical properties of these nanoheterostructures are tunable through the variation of their geometric and compositional parameters. The excited state dynamics in these systems are sensitive to external factors such as temperature, the dielectric properties of the solvent, or the presence of external electric fields.
Entropy Reorders Polariton States Scholes, Gregory D; DelPo, Courtney A; Kudisch, Bryan
The journal of physical chemistry letters,
08/2020, Letnik:
11, Številka:
15
Journal Article
Recenzirano
The main result is that the long-range phase coherence of the polariton states formed by strong coupling between a photon mode in a cavity and an ensemble of molecules leads to exceptionally low ...entropy of the upper and lower polariton states, starkly contrasting with the dark states. That result means that spectroscopy does not correctly order the free energy of the excited states because there is a significant entropic contribution to the free energy, which turns out to comparable to the electronic energy gap between the lower polariton state and the dark-state manifold. The reordered states, according to their free energy, is important to predict the potential of polariton states for reactivity, to predict spontaneous photophysical dynamics, or to understand their decoherence. The entropic contribution adds to the polariton electronic gap, rendering states surprisingly more reactive than anticipated from the input excitation energy. This apparently “additional” reactivity, evident from the thermodynamics, suggests how the low entropy of highly coherent states can be exploited as a resource.
Hybrid organic–inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals ...are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CH3NH3PbI3 and CH3NH3PbBr3 perovskite nanocrystals with an average crystal size of 5.4 ± 0.8 nm and 6.4 ± 1.3 nm, respectively, as confirmed through transmission electron microscopy measurements. Additive-confined perovskite nanocrystals show significantly improved photoluminescence quantum yield and decay lifetime. Finally, we demonstrate highly efficient CH3NH3PbI3 red/near-infrared LEDs and CH3NH3PbBr3 green LEDs based on this strategy, achieving an external quantum efficiency of 7.9% and 7.0%, respectively, which represent a 40-fold and 23-fold improvement over control devices fabricated without the additives.
The current state of understanding of molecular resonance energy transfer (RET) and recent developments in the field are reviewed. The development of more general theoretical approaches has uncovered ...some new principles underlying RET processes. This review brings many of these important new concepts together into a generalization of Förster's original theory. The conclusions of studies investigating the various approximations in Förster theory are summarized. Areas of present and future activity are discussed. The review covers Förster theory for donor-acceptor pairs and electronic coupling for singlet-singlet, triplet-triplet, and superexchange-mediated energy transfer. This includes the transition density picture of Coulombic coupling as well as electronic coupling between molecular aggregates (excitons). Spectral overlaps and ensemble energy transfer rates in disordered aggregates, the role of dielectric properties of the medium, weak versus strong coupling, and new models for energy transfer in complex molecular assemblies are also described.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
AbstactThe growing prevalence of synthetically modified proteins in pharmaceuticals and materials has exposed the need for efficient strategies to enable chemical modifications with high ...site-selectivity. While genetic engineering can incorporate non-natural amino acids into recombinant proteins, regioselective chemical modification of wild-type proteins remains a challenge. Herein, we use photoredox catalysis to develop a site-selective tyrosine bioconjugation pathway that incorporates bioorthogonal formyl groups, which subsequently allows for the synthesis of structurally defined fluorescent conjugates from native proteins. A water-soluble photocatalyst, lumiflavin, has been shown to induce oxidative coupling between a previously unreported phenoxazine dialdehyde tag and a single tyrosine site, even in the presence of multiple tyrosyl side chains, through the formation of a covalent C–N bond. A variety of native proteins, including those with multiple tyrosines, can successfully undergo both tyrosine-specific and single-site-selective labelling. This technology directly introduces aldehyde moieties onto native proteins, enabling rapid product diversification using an array of well-established bioorthogonal functionalization protocols including the alkyne–azide click reaction.Regioselective chemical modification of wild-type proteins remains challenging. Now, by harnessing the varied SOMOphilicity of native tyrosine residues through photoredox catalysis, a site-selective bioconjugation method has been developed. This technology directly incorporates bioorthogonal formyl groups in one step, forming structurally defined fluorescent conjugates that can be rapidly diversified to biorelevant products.
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