Single-molecule spectroscopy was used to follow the orientation of a single probe molecule in a polymer film in real time. Broad spatially heterogeneous dynamics were observed on long time scales, which result from simple diffusive rotational motions on short time scales. This diffusive behavior persists for many rotations before the molecule's local environment changes to one characterized by a new time scale. This environmental exchange occurs instantaneously on the time scale of the experiment and may arise from large-scale collective motions. The distribution of exchange times for these environments was measured for several temperatures near the glass transition.

Single molecule spectroscopy was used to characterize the rotation of fluorescent probe molecules in supercooled o-terphenyl (OTP) just above the glass transition. Rotational motions of spatially isolated individual probe molecules were followed in real time, revealing dynamics that reflect a mosaic of spatially heterogeneous environments. The short-time molecular motions in each environment are found to be diffusional, taking place through a Brownian rotational process characterized by a single rotational correlation time τC. The distribution of rotational diffusion constants for the heterogeneous environments becomes larger as the temperature approaches T g, manifesting increased heterogeneity as OTP is cooled toward the glass transition. After many molecular rotations, the molecule's rotational time changes abruptly. This switch appears instantaneous on the time scale of molecular rotation and is indicative of a rapid rearrangement of the molecule and its local environment. The time required for the environment to change, τEx, is on average 15 times larger than the τC, and nearly 300 times slower than the α-relaxation time in OTP. The ensemble average correlation, 〈τC〉, and exchange times, 〈τEx〉, show a similar temperature dependence, both of which are consistent with the temperature dependence predicted by the Debye Stokes Einstein equation.

A theoretical investigation of the temperature dependence of the optical Kerr effect and Raman spectroscopy of liquid CS 2 A combined instantaneous normal mode and time correlation function description of the optical Kerr effect and Raman spectroscopy of liquid CS 2 A treatment of stimulated Raman intermolecular spectroscopy is presented that employs a Landau-Teller model of damping. This model incorporates a quantum-number dependence to population relaxation and pure dephasing, thereby introducing a specific temperature and frequency dependence into the damping in the intermolecular spectrum. Optical-heterodyne detected Raman-induced Kerr effect data obtained in CS 2 and acetonitrile over a broad temperature range are shown to agree with the basic predictions of the model.

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A novel series of monocarbam compounds exhibiting promising antibacterial activity against multidrug resistant Gram-negative microorganisms is reported, along with the synthesis of one such molecule MC-1 (1). Also reported are structure-activity relationships associated with the in vitro and in vivo efficacy of 1 and related analogues in addition to the hydrolytic stability of such compounds and possible implications thereof.

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Single molecule spectroscopy was used to measure the rotations of fluorescent probe molecules in thin films of poly(methyl acrylate) and poly(n-butyl methacrylate) just above their glass-transition temperatures. By collecting the polarized fluorescence from isolated probe molecules, the rotational diffusion of single molecules was followed in real time. The autocorrelation of these transients yields a nonexponential decay from which the rotational correlation time can be calculated. Molecules reveal a broad distribution of correlation times, which showed a clear dependence on the length of observation. At short times, the spatially heterogeneous nature of these films was reflected in their wide range of correlation times. At longer times, environmental exchanges caused the correlation times to converge on a limiting bulk value. The dynamics were characterized by three time scales: a rotational correlation time (τ c ), an environmental exchange time (τ ex ), and the time scale upon which the distribution of time-averaged single-molecule correlation times converged to the ensembleaveraged limit (τ bulk ). Both τ ex and τ bulk were much longer than τ c , with the ensemble average τ ex being approximately 20 times longer than the average τ c and τ bulk roughly 125 times τ c . All three time scales were found to have the same relatively weak temperature dependence when measured at temperatures 5, 10, and 15 K above the glass transition.