Fluorescence-Encoded Infrared Vibrational Spectroscopy with Single-Molecule Sensitivity.

Single-molecule methods have revolutionized molecular science, but techniques possessing the structural sensitivity required for chemical problems-e.g. vibrational spectroscopy-remain difficult to apply in solution.

Fluorescence-Encoded Infrared Spectroscopy: Ultrafast Vibrational Spectroscopy on Small Ensembles of Molecules in Solution.

Fluorescence-encoded infrared (FEIR) spectroscopy is an ultrafast technique that uses a visible pulse to up-convert information about IR-driven vibrations into a fluorescent electronic population. Here we present an updated experimental approach to FEIR that achieves high sensitivity through confocal microscopy, high repetition rate excitation, and single-photon counting. We demonstrate the sensitivity of our experiment by measuring ultrafast vibrational transients and Fourier transform spectra of increasingly dilute solutions of a coumarin dye.

Single-stage MHz mid-IR OPA using LiGaSand a fiber laser pump source.

We present the design and characterization of a tunable mid-IR optical parametric amplifier (OPA) with a 1 MHz 1033 nm fiber laser pump source. The OPA generates >10  nJ/pulse tunable from 3-7.5 μm with 85-165  cm bandwidth and 140-540 fs pulse durations.

Resolving ultrafast exciton migration in organic solids at the nanoscale.

Effectiveness of molecular-based light harvesting relies on transport of excitons to charge-transfer sites. Measuring exciton migration, however, has been challenging because of the mismatch between nanoscale migration lengths and the diffraction limit. Instead of using bulk substrate quenching methods, here we define quenching boundaries all-optically with sub-diffraction resolution, thus characterizing spatiotemporal exciton migration on its native nanometre and picosecond scales.

Uncovering Single-Molecule Photophysical Heterogeneity of Bright, Thermally Activated Delayed Fluorescence Emitters Dispersed in Glassy Hosts.

Recently developed all-organic emitters used in display applications achieve high brightness by harvesting triplet populations via thermally activated delayed fluorescence. The photophysical properties of these emitters therefore involve new inherent complexities and are strongly affected by interactions with their host material in the solid state. Ensemble measurements occlude the molecular details of how host-guest interactions determine fundamental properties such as the essential balance of singlet oscillator strength and triplet harvesting.

Bringing Far-Field Subdiffraction Optical Imaging to Electronically Coupled Optoelectronic Molecular Materials Using Their Endogenous Chromophores.

We demonstrate that subdiffraction resolution can be achieved in fluorescence imaging of functional materials with densely packed, endogenous, electronically coupled chromophores by modifying stimulated emission depletion (STED) microscopy. This class of chromophores is not generally compatible with STED imaging due to strong two-photon absorption cross sections. Yet, we achieve 90 nm resolution and high contrast in images of clusters of conjugated polymer polyphenylenevinylene-derivative nanoparticles by modulating the excitation intensity in the material.

Multiresonant coherent multidimensional spectroscopy of the vibrationally induced decarboxylation of AOT: deuterium oxide reverse micelles.

The multiresonant coherent multidimensional spectroscopy study of D(2)O in AOT micelles reveals two unexpected features in addition to those expected for D(2)O. These features appear when the excitation pulse time ordering defines either fully coherent Liouville pathways or partially coherent pathways where there are intermediate populations. The features shift as the excitation pulse ordering changes between the two sets of pathways.

Direct chemical vapor deposition of graphene on dielectric surfaces.

Direct deposition of graphene on various dielectric substrates is demonstrated using a single-step chemical vapor deposition process. Single-layer graphene is formed through surface catalytic decomposition of hydrocarbon precursors on thin copper films predeposited on dielectric substrates. The copper films dewet and evaporate during or immediately after graphene growth, resulting in graphene deposition directly on the bare dielectric substrates.