We present results of an extensive x-ray diffraction study of a monolayer of C10F21CH2COOH spread on water (pH2) at 19.1 °C. Lever-rule analysis of the in-plane scattering is used to show that there is a coexistence region between ordered condensed islands and a dilute disordered phase. The coexistence region is found to be bounded by molecular areas of 29 Å2 and 2000±600 Å2, in agreement with the pressure-area isotherm. The molecular tilt of the ordered phase remains unchanged from closest packing (near collapse of the monolayer) throughout the coexistence region, and has a value of 2±3 degrees with respect to the normal to the liquid surface. These results are contrasted with those for hydrocarbon monolayers in which the onset of order in the coexistence region is close to the condensed phase boundary, and the ordered phase is compressible with a continuously variable tilt angle ranging from 30 to 0 deg at closest packing. The differences are attributed to the enhanced chain stiffness of the fluorinated chain. To illustrate this interpretation, preliminary scattering results are presented for a monolayer of C8F17(CH2)4COOH on water, which has some of the features of the aliphatic lipid monolayers. Recent molecular dynamics simulations have been found to reproduce all the important qualitative features of these systems [S. Shin, N. Collazo, and S. A. Rice, J. Chem. Phys. 96, xxxx (1992)].

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This work examines, both experimentally and theoretically, nonradiative decay processes in a series of substituted naphthalenes. We report single vibronic level fluorescence lifetimes and fluorescence excitation spectra of jet-cooled 2-chloronaphthalene, 1- and 2-fluoronaphthalene and 1- and 2-methylnaphthalene over an energy range of about 0–4000 cm−1 in S1. While the 00 nonradiative rates of these molecules vary by a factor of 30, the energy dependences of the nonradiative rates are quite similar. At low vibrational energies the nonradiative rates depend sensitively on the level excited, but in general they increase with energy. As energy increases, the nonradiative rates become less sensitive to the level excited and eventually become almost independent of vibrational energy. We can qualitatively predict this behavior using a thermodynamic formalism which treats the density of states as an intramolecular entropy and avoids the calculation of vibrational coupling terms. In addition we report the fluorescence lifetime of the S1 vibrationless level of 1-chloronaphthalene, and single vibronic level fluorescence spectra of levels up to 1396 cm−1 in 2-chloronaphthalene. Most of the fluorescence excitation and fluorescence spectra show substantial enhancement of the origin inensity and vibrational mode mixing in S1 compared to naphthalene. We briefly discuss these substituent effects and make some tentative assignments of S1 vibrational levels. We also discuss substituent effects on the 00 fluorescence lifetimes. In particular, the order of magnitude increase in the decay rate of 1-chloronaphthalene relative to 2-chloronaphthalene cannot be explained using CNDO/S calculations.

This paper reports extensive measurements of the linewidths of rotational transitions in the Ã 2A2←X̃ 2B1 absorption of ClO2. It is found that: (1) The rate of predissociation is independent of the state of rotation of the initially excited molecule, (2) the rate of predissociation depends on the spin state prepared, being greater for the F1(J = N+1/2) state than for the F2(J = N−1/2) state, (3) for v1<3 the rate of predissociation from the states (v100) is independent of v1, but for v1≳3 the rate increases with v1, and (4) the bending mode is a promoting mode for the predissociation. It is argued that spin–orbit coupling is the dominant interaction between the prepared 2A2 state and the intermediate manifold in this indirect predissociation. Analysis of a model of this process leads to the prediction that, if the prepared and intermediate states have nearly the same geometry, whether the intermediate state is real or nascent, the rate of predissociation should be independent of initial rotational state. Furthermore, it is suggested that the spin–rotation interaction mixes the F1 and F2 states; using a two state analysis, the predicted ratio of rates of dissociation G(F1)/G(F2) = 1.2 is in qualitative agreement with that observed, and the lack of dependence of the ratio on N explained.

Diarylethene photochromes show promise for use in advanced organic electronic and photonic materials with burgeoning considerations for biological applications; however, these compounds typically require UV light for photoswitching in at least one direction, thus limiting their appeal. We here introduce a naphthoquinone-based diarylethene that switches between open and closed forms with visible light. The synthesis of this quinone diarylethene relies on Suzuki methodology, allowing for the inclusion of functional groups not otherwise accessible with current synthetic routes.