Skin structure and age-related changes in human skin were characterized in vivo by applying confocal laser scanning microscopy (CLSM) and optical coherence tomography (OCT). The overall effect of aging skin, derived from studies of volunteers belonging to two age groups, was found to be a significant decrease in the maximum thickness of the epidermis and flattening of the dermo-epidermal junction. At a certain depth in the dermis, well below the basal layer, a reflecting layer of fibrous structure is observed in CLSM images. The location of this layer strongly depends on age and is situated much deeper below the skin surface in younger than in older skin. In addition, large structural changes were observed with age. The OCT images show two bright reflecting layers. The first one is due to scattering at the skin surface. The second band appears to be caused by a layer of fibrous structure in the dermis. Direct comparison of CLSM and OCT suggests that the same fibrous layer is imaged by the two techniques. This layer might be due to the transition between the papillary and reticular dermis. A comparison of CLSM and OCT enables a better understanding of the images.

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The photodissociation reaction of the molecular iodine:arene charge-transfer (CT) complex into an iodine atom and an iodine atom-arene fragment has been investigated using femtosecond pump-probe, resonance Raman, and molecular dynamics simulations. In the condensed phase the reaction proceeds on a time scale of less than 25 fs, in sharp contrast to the gas phase where the excited state lifetime of the complex is about 1 ps. Since little CT resonance enhancement is found in Raman studies on the I 2 -stretch vibration, it is concluded that rapid curve crossing occurs from the CT state to a dissociative surface. Of particular interest is the finding that the polarization anisotropy of the iodine atom:arene (I:ar) photoproduct decays on a time scale of 350 fs both in pure arene solvents as well as in mixed arene/cyclohexane solutions. This latter finding rules out that secondary I:ar complex formation is the main cause of this ultrafast depolarization effect. The initial polarization anisotropy is found to be ∼0.12 in pure mesitylene and ∼0.34 in mixed mesitylene/cyclohexane solutions. Semiempirical configuration-interaction calculations show that, except for the axial CT complex, the transition dipole is aligned almost parallel to the normal of the arene plane. The oscillator strength of the CT transition is found to be maximal in the oblique conformation with the I 2 molecule positioned at an angle of about 30°with respect to the arene normal. This iodine angular dependence of the oscillator strength leads to photoselection of bent I 2 :ar complexes in pump-probe experiments. Molecular dynamics simulations confirm earlier findings that the I 2 :benzene complex is a fragile entity and that it persists only for a few hundred femtoseconds. These simulations also provide the proper time scale for the decay of the polarization anisotropy. The fact that the photoproduct experiences a substantial torque in the dissociation process explains the absence of a cage effect in this reaction.