David F. Eaton

Nonlinear Optical Materials

The current state of materials development in nonlinear optics is summarized, and the promise of these materials is critically evaluated. Properties and important materials constants of current commercial materials and of new, promising, inorganic and organic molecular and polymeric materials with potential in second- and third-order nonlinear optical applications are presented.

Mechanism of coinitiation of photopolymerization of methyl methacrylate by hexaarylbiimidazole—hydrogen-atom donor combinations. The role of electron transfer vs. direct hydrogen-atom abstraction

Abstract The photoinitiated polymerization of methyl methacrylate by combinations of 2-( o -chlorophenyl)-4,5-diphenylimidazolyl dimer ( o -Cl-HABI) and various hydrogen-atom donor coinitiators (cumene, the ethylene ketal of benzaldehyde, dimethylaniline, p -toluenesulfinic acid potassium salt (studied as the complex with 18-crown-6), triethylamine, the mercaptans 2-mercaptobenzthiazole, 2-mercaptobenzoxazole and 2-mercaptobenzimidazole, and the disulfide of 2-mercaptobenzthiazole) was studied. The coinitiators were chosen such that some ( e.g. cumene) can only initiate polymerization by direct hydrogen-atom abstraction from the coinitiator by the photoproduced imidazolyl radical, whereas others ( e.g. dimethylaniline) prefer electron transfer and proton loss pathways to form the initiating radicals. Kinetic studies (measurement of the rates of polymerization, molecular weight determination, calculation of kinetic chain length and rates of initiation) were conducted for all the coinitiators. The mercaptans were examined in detail. Analysis of the results and comparison with the parameters for the unambiguous mechanistic cases demonstrated that the mercaptans react with imidazolyl radicals via electron transfer pathways, not via direct hydrogen-atom abstraction.

Modification of photochemical reactivity by zeolites: arrested molecular rotation of polyenes by inclusion in zeolites

In this work we have utilized faujasite [2] and pentasil [3] zeolites as hosts to carry out phototransformations of several organic molecules. Although they possess completely interconnecting three dimensional pore structures these two types of zeolite have fundamentally different void space topologies (Fig. 1). While the former consists of relatively large and spherical cages (diameter about 13 A; entrance pore diameter about 8 A), the latter contains only interconnecting channels (diameter about 5.5 A).

Modification of photochemical reactivity by zeolites: Location of guests within faujasites by heavy-atom-induced phosphorescence

Abstract Heavy-atom-induced phosphorescence of naphthalene included in faujasites has been observed and evidence obtained for the existence of direct interaction between the heavy metal cations present within the zeolite supercage and the included aromatic guest. Naphthalene when included in faujasites exchanged with rubidium and cesium as cations exhibits intense phosphorescence and possesses short singlet and triplet lifetimes. When adsorbed in faujasites exchanged with lithium, sodium and potassium as cations, naphthalene gives intense fluorescence and weak phosphorescence with long singlet and triplet lifetimes.

Electron transfer processes in imaging

Many photoimaging technologies involve electron-transfer processes in the critical image capture, or light-sensitive, step of the process. This chapter reviews the photochemical and photophysical basis for these processes. The chapter is divided into several major sections: an introduction to basic imaging concepts; a brief discussion of the chemistries and photochemistries involved in conventional silver halide based imaging processes and those involving other semiconductors as primary light absorbers; and sections describing less conventional processes that are based on organic photochemical charge transfer processes (electrophotography, color formation systems, and photopolymerization processes).

Guest-Host Molecular Ensembles for Nonlinear Optics

Abstract This paper discusses structural strategies for assembling bulk materials for nonlinear optics. In part one, we review a strategy, based on the concepts of guest-host inclusion complexation. We incorporate molecules into crystalline environments in which molecular dipoles are assembled into materials for second harmonic generation by polar alignment of the dipoles. In part two, we review the fabrication and properties of optical quality materials for third order nonlinear optics based on nanoscale particles of semiconductors included in polymer media.