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Stepwise two-photon absorption (2PA) processes are becoming an important technique because it can achieve high reductive photochemical reactions with visible and near infrared light and intensity-gated high spatiotemporal selectivity with much lower power thresholds than those of the simultaneous 2PA. However, excited states generated by stepwise 2PA (higher excited states and excited states of transient species) are so short-lived that the efficiency for the stepwise 2PA induced photochemical reactions is usually quite low, which limits the versatility for this technique. Here, we demonstrated that the electron of the higher excited state can be efficiently extracted in a nanohybrid of organic molecules and wide bandgap semiconductor nanocrystals (NCs).1 Using perylene bisimide (PBI)-coordinated CdS NCs as a model compound, we demonstrated that the electron of the higher excited state of PBI generated by stepwise 2PA can be extracted to the conduction band of CdS NCs with a quantum yield of ∼0.5–0.7. Moreover, the extracted electron survives at the conduction band of CdS NCs over nanoseconds, which is more than hundred times longer than the lifetime of the higher excited state of PBI. This method can be applied to other organic molecules and larger wide bandgap semiconductors, and therefore, will expand the versatility for the photochemical reactions utilizing the short-lived excited states.

AIPP Photonics in Chemical Physics

Green and far-red-light induced electron injection from perylene bisimide to wide-bandgap semiconductor nanocrystals with stepwise two-photon absorption process

electron transfer

stepwise two-photon absorption processes

higher excited states

The field of photonics, broadly defined, ranges from basic physical work on lasers and ultrashort laser pulses to applications in healthcare, communications, and materials. With its increasingly diverse disciplines and subdisciplines, photonics has become a key component in modern society. The scientific program consists of cross-disciplinary researchers, including chemists, physicists, and engineers, in both theory and experimentation. These researchers will discuss this rapidly expanding field and cover topics that address the latest advances in photonics related research and debate the current needs and priorities, as well as the emerging areas.

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The field of photonics, broadly defined, ranges from basic physical work on lasers and ultrashort laser pulses to applications in healthcare, communications, and materials. With its increasingly diverse disciplines and subdisciplines, photonics has become a key component in modern society. 

poster

Controlling light-matter interaction with molecular vibrations in mid-infrared resonators offers exciting new research opportunities in chemistry and physics [1]. Laboratory implementations use standard materials, operate at room temperature, and use traditional fabrication and detection techniques, yet they have deeply challenged our fundamental understanding on the connections between cavity quantum electrodynamics and chemistry. We have developed rigorous microscopic quantum theory to describe the optical and chemical properties of realistic molecular vibrations in infrared cavity resonators with non-perturbative light-matter interaction [2,3]. We can successfully describe the linear and nonlinear spectra of vibrational polaritons [4]—hybrid vibration-cavity eigenstates– and realistically study the dissociation dynamics of cavity-coupled molecular bonds under non-adiabatic conditions [5]. The role of symmetry of the ground state electronic density with respect to nuclear displacements in the dynamics of vibrational polaritons is discussed, and future applications of these systems for the generation of THz quantum light are suggested.

Strong light-matter coupling with molecular vibrations in infrared resonators

Donor-bridge-acceptor systems based on boron dipyrromethene (BODIPY) are attractive candidates for bio-imagining and sensing applications because of their sensitivity to temperature, micro-viscosity and solvent polarity. The optimization of the properties of such molecular sensors requires detailed knowledge of the relation between the structure and the photophysical behavior in different environments. In this work, we have investigated the excited-state dynamics of three acceptor-donor-acceptor molecules based on benzodithiophene and BODIPY in solvents of different polarities using a combination of ultrafast spectroscopy and DFT-based electronic structure calculations. Transient absorption spectra show that upon photoexcitation an initial excited species with an induced absorption band in the near-infrared regime is formed independently of the solvent polarity. The subsequent photophysical processes strongly depend on the solvent polarity. In non-polar toluene, this initial excited state undergoes a structural relaxation leading to a delocalized state with partial charge transfer character, while in the more polar tetrahydrofuran a fully charge-separated state is formed. The results clearly show how factors such as donor-acceptor distance and restricted rotational motion by steric hindrance can be used to tune the excited state photophysics to optimize such systems for specific applications.

Excited state dynamics of BODIPY-based acceptor–donor–acceptor systems: a combined experimental and computational study

Effects of electron-vibrational interaction in equilibrium and hot polariton luminescence in microcavities

We found that the time-resolved photoluminescence (TRPL), probed from the imperfection-free CH3NH3PbBr3 crystal bulk, is characterized by a two-stage model (Fig. 1a) that indicates excited phase evolution. Each stage decays following mono-exponential function, and reprents rapid thermal dissociation of the initially generated electron-hole (e-h) pairs and the steady decay of the subsequently formed e-h plamas, respectively. The buffering region (shadowed in red) in between represents the evolving from the dissociated electrons and holes toward the metastable e-h plasmas, similar to previous observations.2 Droplet characters shown by the exciting power threshold (PT) and optically hysteresis are observed (Fig. 1b) for the the largely red-shifted bulk emission with asymmetric spectral line-shape that extends far toward lower energies (inset, Fig. 1a). At certain exciting intensity, the luminescence approached from a more intense exciting power is greater than that reached by in the forward way. We realized and confirmed the occurrence of e-h liquid (EHL) which–most likely–is a cloud of droplets in CH3NH3PbBr3. This not only betters our understanding on halide perovskites but also promotes the search for room-temeprature EHL.3



Excited phase evolution and electron-hole droplets in CH3NH3PbBr3 crystal

An optical microcavity is an interesting tool to study light-matter interaction, e.g. the coupling of a quantum emitter to the optical field in a microcavity. The coupling rate is a measure of the interaction strength between the quantum emitter and cavity mode, and can be used to differentiate between weak or strong coupling.1 
Here, we demonstrate a strongly coupled hybrid system consisting of a thin molecular film of TDBC J-aggregate inside an optical sub-wavelength microresonator coupled to a second microresonator. This hybrid structure combines strong coupling of purely optical modes with strong light-matter interaction.2 The coupling strength and damping of the hybrid system can be tuned by the optical microresonator modes, the lateral position of the TDBC film in the microresonator, and the TDBC concentration in the film. The design of the coupled microresonators allows tuning the resonance of one microcavity across the other, which enables to study the dispersion of the strongly coupled system without tilting of the sample.3 The Rabi splitting of the molecule/cavity hybrid system depends on the position and the number of coherently coupled molecules in the coupled microresonator.2,4 We illustrate this dependence by adjusting the position of TDBC thin film in the coupled microresonator and by reducing the number of molecules by photobleaching. Finally, we will show that the transmission spectrum of the coupled system can be theoretically modeled by coupled damped harmonic oscillators and find an excellent agreement between experiment and theory. 


Combining optical strong mode coupling with polaritonic coupling in a λ/2 Fabry Pérot microresonator

In the advancement of quantum technology, quantum control of photons has received much attention in recent years. In this work, we explore how exciton-exciton interaction and second-order nonlinearity coherently controls the
quantum statistical properties (Photon blockade effect) of photons' in a photonic crystal cavity. We study the second-order correlation analytically and numerically and found that the different physical parameters can effectively tune
the phonon blockade.

Photon blockade effect in a nonlinear photonic crystal cavity.

NMR provides a non-destructive spectroscopic technique for determining the chemical structure of molecules, but its sensitivity is absolutely low because the nuclear spin polarization is low. One method to improve the sensitivity of NMR is Dynamic Nuclear Polarization (DNP). In DNP, the polarization is transferred to nuclear spins from electron spins with a high polarization ratio only at cryogenic temperatures. In contrast, DNP using photo-excited triplet electron spins (triplet-DNP), can achieve high sensitivity of NMR under higher temperature conditions. However, triplet-DNP of biomolecules has not been achieved because conventional acene-based polarizing agents aggregate in hydrophilic biomolecular crystals. Here we report triplet-DNP of erythritol-d4, a hydrophilic molecular crystal using a hydrophilic porphyrin derivative (TCPPNa) as a novel polarizing agent. Interestingly, TCPPNa maintains its triplet electron spin polarization even when it is aggregated in erythritol-d4 crystals. We achieved about 120 times enhancement of the 1H NMR signal intensity of erythritol-d4 by using slightly aggregated TCPPNa.

Triplet Dynamic Nuclear Polarization of Biomolecules Using Porphyrin Aggregates

Trivalent europium ions (Eu(III)) exhibit high color purity, but their absorption coefficients are very small. Eu(III) complexes that utilize energy transfer from antenna ligands to a metal center have been developed to produce efficient luminescent materials. Nevertheless, their energy transfer mechanisms, which depend on the kinds of ligands and their configurations, are still elusive due to weak and complicated interactions between organic ligands and lanthanide ions. To elucidate the energy transfer mechanisms, we measured the temporal changes of emission and absorption spectra using time-resolved photoluminescence (TR-PL) and transient absorption (TA), respectively. We compared the intramolecular energy transfer of the mononuclear complex and the dinuclear complex. Although they have identical antenna chromophores, the dynamics of the two complexes are different. The lifetime of the ligand S1 state in the dinuclear complex is faster than in the mononuclear complex. By comparing molecular geometries between the complexes, we concluded that this difference originated from the difference in the relative configuration of the two triphenylenes. Our discovery helps to establish the design strategy of highly efficient luminescent lanthanide complexes in photofunctional materials.

Energy transfer dynamics in luminescent Eu(III) complexes with phosphine oxide ligands


In this study, optical deep-level transient spectroscopy (O-DLTS) has been employed to investigate trap properties in the p-GaN/AlGaN heterostructure, the key part of such a normally-off enhancement-mode III-N transistors. Three electron traps labeled as E1, E2, and E3 were extracted by O-DLTS. The temperature-enhanced emission process of E3 has been studied by isothermal mode O-DLTS.



Study of Traps in p-GaN Gate HEMT by Optical DLTS

The new trends in biosensing field involves fast and real-time identification of biomarkers for rapid diagnosis with less-invasive methods by means of low-cost miniaturized and portable point of care devices. The ability of plasmonic systems to confine the light at nanometer dimension and manipulate the light with size, shape and material features, makes these systems promising candidates for biomedical devices. In this work we demonstrate the sensing capability of compact arrays of 3D metal dielectric core-shell chiral nano helices-based metamaterial enabled by the engineering of many technological elements. On one hand, the intrinsic chiral geometry of these structures, realized by Focused Ion Beam Induced Deposition technology, makes the system unaffected by background interferences, allowing to work even in optically dense environments like body fluids. Moreover, the metal-dielectric architecture realized through a conformal coating of a functional polymeric layer, enhance the chiroptical plasmonic properties of the chiral metamaterial in the far and near- field, and offers a large surface to suitable for molecular immobilization, together with the extrusion along the third dimension. We recorded refractive index sensitivity of about 800nm/RIU and FOM= 1276 RIU-1 for different concentration of glycerol-water solution. We also demonstrated the detection abilities to surface-specific binding event with the Tar-Dna binding protein, TDP-43, currently under study as biomarker for early-stage detection of neurodegenerative diseases. We successfully tested the sensor at different molar concentrations ranging from 1pM down to 10 fM, and in different environment, like human serum. We believe that our finding provides new perspectives for novel diagnostic tools.

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Green and far-red-light induced electron injection from perylene bisimide to wide-bandgap semiconductor nanocrystals with stepwise two-photon absorption process

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Strong light-matter coupling with molecular vibrations in infrared resonators

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