Time-resolved energy transfer from single chloride terminated nanocrystals to graphene

We examine the time-resolved resonance energy transfer of excitons from single n-butyl amine-bound, chloride-terminated nanocrystals to two-dimensional graphene through time-correlated single photon counting. The radiative biexponential lifetime kinetics and blinking statistics of the individual surface-modified nanocrystal elucidate the non-radiative decay channels. Blinking modification as well as a 4 times reduction in spontaneous emission were observed with the short chloride and n-butylamine ligands, probing the energy transfer pathways for the development of graphene-nanocrystal nanophotonic devices

Conformational rearrangements in and twisting of a single molecule

Single molecule spectroscopy is used to obtain detailed information on the photophysical properties of immobilized perylenediimide-based molecules, substituted in the bay positions. The fluorescence spectra recorded for numerous single molecules show a clear bimodal distribution of the peak position. Within the low energy component of the distribution, two different vibronic shapes of the emission spectrum can be seen, which can be correlated to different decay times. We show that former observation can be explained by conformational changes of the bay substituents while the latter are related to twisting of the single molecule around the central perylenediimide long axis

Dynamics of the dispersion interaction in an energy transfer system

On the propagation of resonant radiation through an optically dense system, photon capture is commonly followed by one or more near-field transfers of the resulting optical excitation. The process invokes secondary changes to the local electronic environment, shifting the electromagnetic interactions between participant chromophores and producing modified intermolecular forces. From the theory it emerges that energy transfer, when it occurs between chromophores with electronically dissimilar properties, can itself generate significant changes in the intermolecular potentials. This report highlights specific effects that can be anticipated when laser light propagates across an interface between differentially absorbing components in a model energy transfer system

Generation-Dependent Energy Dissipation in Rigid Dendrimers Studied by Femtosecond to Nanosecond Time-Resolved Fluorescence Spectroscopy

Intramolecular kinetic processes in a series of second- generation polyphenyl dendrimers with multiple peryleneimide chromophores attached to the para position of the outer phenyl ring were investigated by steady-state and femtosecond to nanosecond time-resolved fluorescence spectroscopy. The results obtained were compared to the ones of the corresponding first- generation dendrimer series. The energy-hopping rate constant, k(hopp), observed from anisotropy decay times was found to be 5 times smaller than that of the first-generation series and scales well with the difference in average distance between the chromophores. In addition to the processes observed in first- generation dendrimers in the ultrafast time domain by fluorescence up-conversion, a second. annihilation process is found in the second-generation multichromophoric dendrimer. The observation of two singlet-singlet annihilation processes in this compound can be explained by the presence of a mixture of constitutional isomers leading to a broader distribution of distances between neighboring chromophores compared to first- generation multichromophoric dendrimers

mKikGR, a Monomeric Photoswitchable Fluorescent Protein

The recent demonstration and utilization of fluorescent proteins whose fluorescence can be switched on and off has greatly expanded the toolkit of molecular and cell biology. These photoswitchable proteins have facilitated the characterization of specifically tagged molecular species in the cell and have enabled fluorescence imaging of intracellular structures with a resolution far below the classical diffraction limit of light. Applications are limited, however, by the fast photobleaching, slow photoswitching, and oligomerization typical for photoswitchable proteins currently available. Here, we report the molecular cloning and spectroscopic characterization of mKikGR, a monomeric version of the previously reported KikGR that displays high photostability and switching rates. Furthermore, we present single-molecule imaging experiments that demonstrate that individual mKikGR proteins can be localized with a precision of better than 10 nanometers, suggesting their suitability for super-resolution imaging

Fermi polaron-polaritons in charge-tunable atomically thin semiconductors

The dynamics of a mobile quantum impurity in a degenerate Fermi system is a fundamental problem in many-body physics. The interest in this field has been renewed due to recent ground-breaking experiments with ultracold Fermi gases. Optical creation of an exciton or a polariton in a two-dimensional electron system embedded in a microcavity constitutes a new frontier for this field due to an interplay between cavity coupling favouring ultralow-mass polariton formation6 and exciton–electron interactions leading to polaron or trion formation. Here, we present cavity spectroscopy of gate-tunable monolayer MoSe2 exhibiting strongly bound trion and polaron resonances, as well as non-perturbative coupling to a single microcavity mode. As the electron density is increased, the oscillator strength determined from the polariton splitting is gradually transferred from the higher-energy repulsive exciton-polaron resonance to the lower-energy attractive exciton-polaron state. Simultaneous observation of polariton formation in both attractive and repulsive branches indicates a new regime of polaron physics where the polariton impurity mass can be much smaller than that of the electrons. Our findings shed new light on optical response of semiconductors in the presence of free carriers by identifying the Fermi polaron nature of excitonic resonances and constitute a first step in investigation of a new class of degenerate Bose–Fermi mixtures.Physic