Search

N,N-dimethylaminobenzylidene 1,3-indandione (DMABI) was considered. The formation of charge transfer excitonstates in the absorption and luminescence spectra by increase of the thicknesses of DMABI films was observed. Theevidence of a strong exciton-phonon interaction and its effects on the exciton absorption and luminescence spectra wasdiscovered. The coexistence of free and self-trapped excitons at elevated temperatures was found in DMABI films. Thedynamics of both shallow short-lived and deeply trapped long-lived self-trapped exciton states in various films andcrystal of DMABI was discussed.Keywords: molecular crystals, N,N-dimethylaminobenzylidene 1 ,3 -indandione, spectroscopy, luminescence,self-trapped excitons, charge transfer1. INTRODUCTIONThe dipole moment of the electronic transition is the main parameter determining the excitonic feature of thespectrum of molecular crystals. The presence of steady-state dipole moments in the ground and excited molecularstates creates the interaction with other molecules of the surrounding. By means of the exciton theory, the latter causesan essential increase of the displacement gy'2 in comparison with the classical crystals and, moreover, strongelectron-phonon or electron-vibrational modes interaction cannot be treated perturbatively anymore. The dispersiveinteraction is responsible for absorption band shifts depending to the polarity of solvents or by modifying the crystalstructure, while strong electron-phonon interactions can create a distinct Stokes-shift of the fluorescence band. Due tothose interactions the spectral properties of polar systems become very sensitive to the structural changes, differenciesin temperature and excitation conditions, and these systems can express optically non-linear behaviour in somespectral regions.3 Therefore, new possibilities of their application to non-linear optics and molecular electronics are

Organic molecular materials displaying effective optical second harmonic generation (SHG) is of major interest in molecular engineering and non-linear optics. In this review synopsis of experimental and theoretical studies of photoactive molecular multilayer Langmuir-Blodgett (LB) films of oriented dipolar betaine type organic molecules is presented and the pathways of search of new indandione-1,3, pyridinium betaine (IPB) derivatives with enhanced second- order non-linear response are discussed. Characterization of highly dipolar betaine-type molecules, with IPB molecule as a prototype, has been presented and conditions of effective SH generation discussed. Molecular structure, phase transitions and optical properties of monolayers of amphiphilic IPB derivatives on the water/air interface have been discussed. Electronic and both linear and non-linear optical properties of LB multilayer molecular assemblies of amphiphilic IPB derivatives have been discussed. New developments in molecular engineering in search for new molecular compounds with high SHG response have also been briefly discussed.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.