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The phase of the molecular response can be exploited to improve selectivity without sacrificing speed in both narrowband and broadband coherent anti-Stokes Raman scattering (CARS) microscopy, both of which will be considered in this review of the work that was performed in our group.

In coherent anti-Stokes Raman scattering (CARS), the emitted signal carries both amplitude and phase information of the molecules in the focal volume. Most CARS experiments ignore the phase component, but its detection allows for two advantages over intensity-only CARS. First, the pure resonant response can be determined, and the nonresonant background rejected, by extracting the imaginary component of the complex response, enhancing the sensitivity of CARS measurements. Second, selectivity is increased via determination of the phase and amplitude, allowing separation of individual molecular components of a sample even when their vibrational bands overlap. Here, using vibrational phase contrast CARS (VPC-CARS), we demonstrate enhanced sensitivity in quantitative measurements of ethanol/methanol mixtures and increased selectivity in a heterogeneous mixture of plastics and water. This powerful technique opens a wide range of possibilities for studies of complicated systems where overlapping resonances limit standard methodologies. 10.1021/ac101453s

Dissolution testing is a crucial part of pharmaceutical dosage form investigations and is generally performed by analyzing the concentration of the released drug in a defined volume of flowing dissolution medium. As solid-state properties of the components affect dissolution behavior to a large and sometimes even unpredictable extent there is a strong need for monitoring and especially visualizing solid-state properties during dissolution testing. In this study coherent anti-Stokes Raman scattering (CARS) microscopy was used to visualize the solid-state properties of lipid-based oral dosage forms containing the model drug theophylline anhydrate during dissolution in real time. The drug release from the dosage form matrix was monitored with a spatial resolution of about 1.5 [micro]m. In addition, as theophylline anhydrate tends to form the less soluble monohydrate during dissolution, CARS microscopy allowed the solid-state transformation of the drug to be spatially visualized. The results obtained by CARS microscopy revealed that the method used to combine lipid and active ingredient into a sustained release dosage form can influence the physicochemical behavior of the drug during dissolution. In this case, formation of theophylline monohydrate on the surface was visualized during dissolution with tablets compressed from powdered mixtures but not with solid lipid extrudates.

The nature of the electronic excited states and their dynamics and coupling to the nuclear degrees of freedom in antennae of photosynthetic purple bacteria are considered. It was found that, in addition to the fast exciton relaxation, a set of slower processes occurs in B850 at low temperatures.

Carotenoids are involved in a variety of biological functions, yet the underlying mechanisms are poorly understood, in part because of the long-standing difficulty in assigning the location of the first excited ([S.sub.1]) state. Here, we present a method for determining the energy of the forbidden [S.sub.1] state, on the basis of ultrafast spectroscopy of the short lived level. Femtosecond transient absorption spectra and kinetics of the [S.sub.1] [approaches] [S.sub.2] transition revealed the location of the intermediate level in two carotenoid species involved in the xanthophyll cycle, zeaxanthin and violaxanthin, and yielded surprising implications regarding the mechanism of photoregulation in photosynthesis.

The concept of ergodicity in molecules is cenTral to chemical reactivity. Given the complexity of molecules with numerous degrees of freedom, vibration, and rotation, how would a deposited energy (E) […]

We report transient absorption spectroscopic studies on the hybrid material composed of porphyrin molecules covalently attached to graphene for investigating the mechanism underlying the reported fluorescence quenching of porphyrin in the hybrid [1]. Excited state dynamics of pure graphene suspension and porphyrin have also been studied as reference samples. A fast excited state decay was observed in the hybrid.

A series of all-trans-carotenoids with N=9, 13, and 15 conjugated bonds has been studied by pump-probe and pump-deplete-probe spectroscopies to obtain a systematic analysis of the energy flow between the different electronic states. The ultrafast dynamics in the carotenoids are initialized by excitation to the S2 state and subsequently manipulated by an additional depletion pulse in the near-IR spectral range. The changes in the dynamics after depletion of the excited state population allowed differentiation of the excited state absorption into two components, a major one corresponding to the well known S1 state and the small contribution on the red wing of the S0-S2 absorption band originating from the hot ground state. We found no evidence for an additional electronically excited state, usually called S*. Instead, a deactivation mechanism that includes the hot ground state supports the observed results nicely in the framework of a simple three state model (S2, S1, and S0). [ABSTRACT FROM AUTHOR]

The bioinspired dyad molecule is studied by using time-resolved spectroscopies and its structure, spectrum and dynamics is compared to the LH2 complex from Rhodopseudomonas acidophila. The caroteno-purpurin dyad is found to be an ideal case for the coherent-control study, as it has a clear branching of the energy flow between two competing pathways leading to two different processes, energy transfer (ET) and loss channel (IC).