Luminescence and nonlinear optical properties of substituted cinnamoylquinolines

Abstract

and were obtained by the condensation of 3-acetyl-2,4-dihydroxyquinoline (2) with the appropriate aldehydes, with quan- titative yields; the structures of the compounds were confirmed by IR and mass spectrometric data. We investigated the properties of the cinnamoylquinolines in the form of crystalline powder and thin films. The films were deposited on quartz substrates by thermal vaporization in vacuum. The film thickness was 0.10-0.15 #m. For some of the compounds, the spectral and luminescence characteristics of the crystalline powders and films are shown in Fig. 1. With UV excitation, we observed intense luminescence from powders of compounds I-III owing to the presence of the electron-donor groups -N(CH3) 2 and -OCH 3 in the ortho and para positions. The presence of electron-acceptor groups in these positions led to disappearance of the charges on the ends of the conjugation chain, resulting in a decrease of quantum efficiency of the luminescence of compounds IV, VI, and VII, and in the case of compound V to the complete absence of luminescence. The luminescence bands of substances in the form of thin films were broadened in comparison with the luminescence bands of the crystalline powders, as a consequence of nonuniformity of aggregation of the molecules (3). The luminescence spectra of all of the cinnamoylquinoline derivatives that we studied exhibit abnormally large Stokes shifts (about 150 nm), owing to energy losses in proton transfer and a change in strength of the intramolecular hydrogen bond in the excited state (4). Since such molecular structures are characteristic for substances with highly nonlinear susceptibility, we carried out studies of the nonlinear optical properties of a number of the compounds that we had synthesized. With excitation of the powdered substances by radiation of a neodymium laser (~gen = 1064 nm, generation pulse length rpu I = 10 nsec, single pulse energy Epu I - 15 mJ), we registered radiation of the second harmonic with X = 532 nm for all of the synthesized compounds. For compounds I and II, along with the second harmonic we observed luminescence in