6,756 research outputs found
Inverting Singlet and Triplet Excited States using Strong Light-Matter Coupling
In organic microcavities, hybrid light-matter states can form with energies
that differ from the bare molecular excitation energies by nearly 1 eV. A
timely question, given recent advances in the development of thermally
activated delayed fluorescence materials, is whether strong light-matter
coupling can be used to invert the ordering of singlet and triplet states and,
in addition, enhance reverse intersystem crossing (RISC) rates. Here, we
demonstrate a complete inversion of the singlet lower polariton and triplet
excited states. We also unambiguously measure the RISC rate in strongly-coupled
organic microcavities and find that, regardless of the large energy level
shifts, it is unchanged compared to films of the bare molecules. This
observation is a consequence of slow RISC to the lower polariton due to the
delocalized nature of the state across many molecules and an inability to
compete with RISC to the dark exciton reservoir, which occurs at a rate
comparable to that in bare molecules
Triplet harvesting in the polaritonic regime: a variational polaron approach
We explore the electroluminescence efficiency for a quantum mechanical model
of a large number of molecular emitters embedded in an optical microcavity. We
characterize the circumstances under which a microcavity enhances harvesting of
triplet excitons via reverse intersystem-crossing (R-ISC) into singlet
populations that can emit light. For that end, we develop a time-local master
equation in a variationally optimized frame which allows for the exploration of
the population dynamics of chemically relevant species in different regimes of
emitter coupling to the condensed phase vibrational bath and to the microcavity
photonic mode. For a vibrational bath that equilibrates faster than R-ISC (in
emitters with weak singlet-triplet mixing), our results reveal that significant
improvements in efficiencies with respect to the cavity-free counterpart can be
obtained for strong coupling of the singlet exciton to a photonic mode, as long
as the singlet to triplet exciton transition is within the inverted Marcus
regime; under these circumstances, we show the possibility to overcome the
detrimental delocalization of the polariton states across a macroscopic number
of molecules. On the other hand, for a vibrational bath that equilibrates
slower than R-ISC (i.e., emitters with strong singlet-triplet mixing), we find
that while enhancemnents in photoluminiscence can be obtained via vibrational
relaxation into polaritons, this only occurs for small number of emitters
coupled to the photon mode, with delocalization of the polaritons across many
emitters eventually being detrimental to electroluminescence efficiency. These
findings provide insight on the tunability of optoelectronic processes in
molecular materials due to weak and strong light-matter coupling
Measuring kinetic energy changes in the mesoscale with low acquisition rates
We describe a new technique to estimate the mean square velocity of a
Brownian particle from time series of the position of the particle sampled at
frequencies several orders of magnitude smaller than the momentum relaxation
frequency. We apply our technique to determine the mean square velocity of
single optically trapped polystyrene microspheres immersed in water. The
velocity is increased applying a noisy electric field that mimics a higher
kinetic temperature. Therefore, we are able to measure the average kinetic
energy change in isothermal and non-isothermal quasistatic processes. Moreover,
we show that the dependence of the mean square time-averaged velocity on the
sampling frequency can be used to quantify properties of the electrophoretic
mobility of a charged colloid. Our method could be applied to detect
temperature gradients in inhomogeneous media and to characterize the complete
thermodynamics of microscopic heat engines.Comment: 9 pages, 5 figure
Can ultrastrong coupling change ground state chemical reactions?
Recent advancements on the fabrication of organic micro- and nanostructures
have permitted the strong collective light-matter coupling regime to be reached
with molecular materials. Pioneering works in this direction have shown the
effects of this regime in the excited state reactivity of molecular systems and
at the same time has opened up the question of whether it is possible to
introduce any modifications in the electronic ground energy landscape which
could affect chemical thermodynamics and/or kinetics. In this work, we use a
model system of many molecules coupled to a surface-plasmon field to gain
insight on the key parameters which govern the modifications of the
ground-state Potential Energy Surface (PES). Our findings confirm that the
energetic changes per molecule are determined by single-molecule-light
couplings which are essentially local, in contrast with those of the
electronically excited states, for which energetic corrections are of a
collective nature. Still, we reveal some intriguing quantum-coherent effects
associated with pathways of concerted reactions, where two or more molecules
undergo reactions simultaneously, and which can be of relevance in low-barrier
reactions. Finally, we also explore modifications to nonadiabatic dynamics and
conclude that, for this particular model, the presence of a large number of
dark states yields negligible changes. Our study reveals new possibilities as
well as limitations for the emerging field of polariton chemistry
Adiabatic processes realized with a trapped Brownian particle
We experimentally realize quasistatic adiabatic processes using a single
optically-trapped micro- sphere immersed in water whose effective temperature
is controlled by an external random electric field. A full energetic
characterization of adiabatic processes that preserve either the position dis-
tribution or the full phase space volume is presented. We show that only in the
latter case the exchanged heat and the change in the entropy of the particle
vanish when averaging over many repetitions. We provide analytical expressions
for the distributions of the fluctuating heat and en- tropy, which we verify
experimentally. We show that the heat distribution is asymmetric for any
non-isothermal quasistatic process. Moreover, the shape of the distribution of
the system entropy change in the adiabatic processes depends significantly on
the number of degrees of freedom that are considered for the calculation of
system entropy
Riesgo de resultados negativos asociados a inhibidores de la bomba de protones: revisión de las prescripciones electrónicas en pacientes polimedicados
Introducción: El elevado consumo de inhibidores de la bomba de protones (IBP) puede incrementar la probabilidad de aparición de interacciones clÃnicamente relevantes. Pacientes mayores, polimedicados y pluripatológicos representan un grupo de alto riesgo. Se espera que la revisión sistemática de las prescripciones electrónicas (PE) permita detectar potenciales interacciones farmacológicas.Material y métodos: Estudio retrospectivo, transversal y observacional: revisión de las PE de IBP dispensadas entre enero y diciembre de 2015 en una farmacia comunitaria rural.Resultados: 1.186 PE, 164 pacientes (edad 65,7±17,2). Mayor número de pacientes en rango de edad 71-80 (n=52). Medicamentos por paciente: 11,0±5,6. PE IBP sin indicación aprobada: 27%.  Indicación mayoritaria: protección frente a gastrolesión (77%). 29 pacientes (30%) con riesgo de resultados negativos asociados a la medicación (RNM) por omeprazol, 15 de ellos sin indicación. PatologÃas concomitantes más prevalentes: hipertensión arterial (n=81), dislipemia (n=61) y diabetes (n=36). Principios activos implicados: acenocumarol, hierro, cianocobalamina, escitalopram, benzodiazepinas y clopidogrel.Discusión: El 80% de las PE de omeprazol corresponde a pacientes entre 61 y 90 años, la mayorÃa con comorbilidad y polifarmacia, y supera el tiempo de tratamiento recomendado. Relacionamos la cronificación y el aumento del riesgo de RNM con la ausencia de un seguimiento adecuado.Muchos fármacos corresponsables del riesgo tratan los problemas de salud (PS) más prevalentes de nuestra población: la probabilidad de interacción resulta independiente de la correcta indicación del IBP.Conclusiones: La revisión de las PE permite valorar el riesgo de RNM y evaluar la información básica relativa al riesgo de interacción.Se detectaron RNM de no necesidad y de inseguridad en proporciones comparables. Un número elevado de PE de omeprazol tienden a cronificarse. Las interacciones más relevantes  registradas ocurren a nivel metabólico
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