Singlet fission is an important candidate to increase energy conversion efficiency in organic photovoltaics by providing a pathway to increase the quantum yield of excitons per photon absorbed in ...select materials. We investigate the dependence of exciton quantum yield for acenes in the strong light-matter interaction (polariton) regime, where the materials are embedded in optical microcavities. Starting from an open-quantum-systems approach, we build a kinetic model for time-evolution of species of interest in the presence of singlet quenchers and show that polaritons can decrease or increase exciton quantum yields compared to the cavity-free case. In particular, we find that hexacene, under the conditions of our model, can feature a higher yield than cavity-free pentacene when assisted by polaritonic effects. Similarly, we show that pentacene yield can be increased when assisted by polariton states. Finally, we address how various relaxation processes between bright and dark states in lossy microcavities affect polariton photochemistry. Our results also provide insights on how to choose microcavities to enhance similarly related chemical processes.
Molecular polaritons are the optical excitations which emerge when molecular transitions interact strongly with confined electromagnetic fields. Increasing interest in the hybrid molecular-photonic ...materials that host these excitations stems from recent observations of their novel and tunable chemistry. Some of the remarkable functionalities exhibited by polaritons include the ability to induce long-range excitation energy transfer, enhance charge conductivity, and inhibit or accelerate chemical reactions. In this review, we explain the effective theories of molecular polaritons which form a basis for the interpretation and guidance of experiments at the strong coupling limit. The theoretical discussion is illustrated with the analysis of innovative applications of strongly coupled molecular-photonic systems to chemical phenomena of fundamental importance to future technologies.
Strong coupling of molecules with confined electromagnetic fields provides novel strategies to control chemical reactivity and spectroscopy.
Strong-coupling between light and matter produces hybridized states (polaritons) whose delocalization and electromagnetic character allow for novel modifications in spectroscopy and chemical ...reactivity of molecular systems. Recent experiments have demonstrated remarkable distance-independent long-range energy transfer between molecules strongly coupled to optical microcavity modes. To shed light on the mechanism of this phenomenon, we present the first comprehensive theory of polariton-assisted remote energy transfer (PARET) based on strong-coupling of donor and/or acceptor chromophores to surface plasmons. Application of our theory demonstrates that PARET up to a micron is indeed possible. In particular, we report two regimes for PARET: in one case, strong-coupling to a single type of chromophore leads to transfer mediated largely by surface plasmons while in the other case, strong-coupling to both types of chromophores creates energy transfer pathways mediated by vibrational relaxation. Importantly, we highlight conditions under which coherence enhances or deteriorates these processes. For instance, while exclusive strong-coupling to donors can enhance transfer to acceptors, the reverse turns out not to be true. However, strong-coupling to acceptors can shift energy levels in a way that transfer from acceptors to donors can occur, thus yielding a chromophore role-reversal or "carnival effect". This theoretical study demonstrates the potential for confined electromagnetic fields to control and mediate PARET, thus opening doors to the design of remote mesoscale interactions between molecular systems.
Exciton-polaritons are quasiparticles with mixed photon and exciton character that demonstrate rich quantum phenomena, novel optoelectronic devices and the potential to modify chemical properties of ...materials. Organic materials are of current interest as active materials for their ability to sustain exciton-polaritons even at room temperature. However, within organic optoelectronic devices, it is often the 'dark' spin-1 triplet excitons that dominate operation. These triplets have been largely ignored in treatments of polaritons, which instead only consider the role of states that directly and strongly interact with light. Here we demonstrate that these 'dark' states can also play a major role in polariton dynamics, observing polariton population transferred directly from the triplet manifold
via
triplet-triplet annihilation. The process leads to polariton emission that is longer-lived (>μs) even than exciton emission in bare films. This enhancement is directly linked to spin-2 triplet-pair states, which are formed in films and microcavities by singlet fission or triplet-triplet annihilation. Such high-spin multiexciton states are generally non-emissive and cannot directly couple to light, yet the formation of polaritons creates for them entirely new radiative decay pathways. This is possible due to weak mixing between singlet and triplet-pair manifolds, which - in the strong coupling regime - enables direct interaction between the bright polariton states and those that are formally non-emissive. Our observations offer the enticing possibility of using polaritons to harvest or manipulate population from states that are formally dark.
Exciton-polaritons are quasiparticles with mixed photon and exciton character with the potential to modify chemical properties of materials. Here, they are used to provide dark, high-spin triplet-pair states a new pathway to emit light.
I study the overstatement of economic growth in autocracies by comparing self-reported GDP figures to night-time light recorded by satellites from outer space. I show that the night-time-light ...elasticity of GDP is larger in authoritarian regimes, even accounting for differences in multiple country characteristics. This autocracy gradient in the elasticity is greater when the incentive to exaggerate economic growth is stronger or when the constraints on exaggeration are weaker. The results suggest that autocracies overstate yearly GDP growth by approximately 35%. Adjusting the data for manipulation leads to a more nuanced view on the recent economic success of autocracies.
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 the 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.
Opinion dynamics investigates the fusion process of the opinion formation in a group of agents, and is a powerful tool for supporting the management of public opinions. However, in real-life ...situations, firms or administrations are not only interested in the formation of public opinions, but also hope to influence and guide the forming opinions to reach either a consensus or even more a specific consensus point. This paper aims at developing a consensus building process in opinion dynamics, based on the concept leadership, by analyzing the structure of the social network in which all agents can form a consensus. It is then proposed a strategy adding a minimum number of interactions in the social network to form a consensus based on leadership, and afterwards it is generalized the consensus strategy to deal with the consensus problem with an established target. Eventually, detailed theoretical proofs and numerical analysis are provided to demonstrate the feasibility and effectiveness of the consensus strategy.
In the past few years, cancer immunotherapy has emerged as a safe and effective alternative for treatment of cancers that do not respond to classical treatments, including those types with high ...aggressiveness. New immune modulators, such as cytokines, blockers of CTLA-4 (cytotoxic T-lymphocyte-associated protein 4) and PD-1(programmed cell death protein 1)/PD-L1 (programmed death-ligand 1), and interaction or adoptive cell therapy, have been developed and approved to treat solid and hematologic carcinomas. In these scenarios, cytotoxic lymphocytes (CL), mainly cytotoxic T cells (Tc) and natural killer (NK) cells, are ultimately responsible for killing the cancer cells and eradicating the tumor. Extensive studies have been conducted to assess how Tc and NK cells get activated and recognize the cancer cell. In contrast, few studies have focused on the effector molecules used by CLs to kill cancer cells during cancer immunosurveillance and immunotherapy. In this article, the two main pathways involved in CL-mediated tumor cell death, granule exocytosis (perforin and granzymes) and death ligands, are briefly introduced, followed by a critical discussion of the molecules involved in cell death during cancer immunosurveillance and immunotherapy. This discussion also covers unexpected consequences of proinflammatory and survival effects of granzymes and death ligands and recent experimental evidence indicating that perforin and granzymes of CLs can activate nonapoptotic pathways of cell death, overcoming apoptosis defects and chemoresistance. The consequences of apoptosis versus other modalities of cell death for an effective treatment of cancer by modulating the patient immune system are also briefly discussed. See all articles in this CCR Focus section, "Cell Death and Cancer Therapy."
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