The considerable activity in the area of organic thin films, involving very thin polymeric films and molecular monolayers and multilayers, led to the formation of a panel, sponsored by the Materials Sciences Division of the Department of Energy, to review this field. Its purpose was to better understand the relevant scientific topics and to suggest suitable areas of research. In particular, a number of potential applications were identified, which require further scientific advances for them to see fruition. These include nonlinear and active optical devices, chemical, biochemical, and physical sensors, protective layers (e.g., for passivation), patternable materials both for resists and for mass information storage, surface modification (e.g., wetting and electrochemical electrode properties), and synthetic biomacromolecules. Studies of these films have the added advantage that they could lead to a better scientific understanding of such subjects as the relationships between the microstructure of ordered molecular arrays and their collective properties, the tailoring of interfaces and surfaces, especially when used to model multibody interactions, and the physical and chemical reactions of films involving phase transitions and intraand interfilm transport. The areas that appear to require the most attention include the application of new characterization techniques, such as the scanning tunneling microscope, the improvement of mechanical and thermal stability, the identification and characterization of physical and chemical defects, and the effects of internal ordering on macroscopic properties. It is further recommended that strong interdisciplinary efforts be mounted to address and solve these problems.

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The preparation of two types of anthracene dimer is described and their absorption and fluorescence spectra are reported. The basic spectral features of each dimer, together with a consideration of the method of formation, enable us to assign a geometry to each pair. One dimer, prepared by photolytic dissociation of dianthracene, has a symmetrical sandwich configuration. The geometry of the other dimer, prepared in solution at low temperatures, is deduced from an analysis of the vibronic structure of its first absorption band (1A1g→1B2u transition of a single molecule) using the theory of vibronic coupling in dimers. The two molecules have a configuration related to that of the two molecules in the unit cell of the crystal; one in which the short in-plane axes make an angle of 55 deg with each other while the long axes are parallel. The resonance splittings of the 1B2u and 1B3u states in each dimer are deduced from the spectra and the results are discussed in relation to the theories of the energy levels of dimers. The fluorescence of the sandwich dimer is of the excimer type while the fluorescence from the other dimer is excited dimer emission with a vibrational intensity distribution different from that in the corresponding monomer spectrum.

The fluorescence spectra of various dinaphthylalkanes have been studied over the temperature range -100-lOOo. Strong intramolecular excimer formation is found only in the two symmetrical 1,3-dinaphthylpropanes, which implies that the stable excimer configuration is the symmetrical sandwich arrangement. Thermally activated self-quenching of fluorescence is important only in the two species which form stable excimers. The quenching path probably does not involve intersystem crossing to a triplet state and transient photodimer formation is suggested .he question of the geometry of an excimer con-(7) E. A. Chandross, E.