Optical absorption of 1,3-diphenyl-1H-Pyrazolo[3,4-b]quinoline and its derivatives S. Całus a , E. Gondek b , A. Danel c , B. Jarosz c , A.V. Kityk d, * a Department of Electrical Engineering, Technical University of Czestochowa, Armii Krajowej 17, 42-200 Czestochowa, Poland b Institute of Physics, Technical University of Krakow, Podhorazych 1, 30-084 Krakow, Poland c Department of Chemistry, Hugon Kollotaj Agricultural University, Al. Mickiewicza 24/28, 30-059 Krakow, Poland d Institute for Computer Science, Technical University of Czestochowa, Armii Krajowej 17, 42-200 Czestochowa, Poland Received 13 May 2006; received in revised form 4 July 2006; accepted 5 July 2006 Abstract Paper deals with the experimental investigations and quantum chemical calculations of the absorption spectra of newly synthesized 1,3-diphenyl-1H-Pyrazolo[3,4-b]quinoline and its 6-Vinyl, 6-N,N-Diphenyl, 6-Methyl, 6-Fluoro, 6-Bromo, and 6-Chloro derivatives. The calculations are performed by means of the semiempirical quantum chemical methods AM1 or PM3 combined with: (a) equilibrium molecular conformation (EMC) in vacuo; (b) the molecular conformation model considering a dynamical rotation of phenyl rings only (T = 300 K); and (c) the most general model of the conformational molecular dynamics (MD) at T = 300 K. It is shown that the phenyl dynamics appears to be not important in the spectral position of absorption thresholds as well as in a broadening of most absorbtion bands. On the other hand, the MD simulations reproduce a broadening of the absorbtion spectra as well as the electron-vibronic cou- pling leading to a red-shift of absorption bands with increasing of temperature. The conformational MD model in combination with the quantum chemical AM1 method gives in most cases the best agreement with the experimental data, namely in the sense of spectral posi- tions and width of the absorption bands including first oscillators (absorption thresholds). Ó 2006 Elsevier B.V. All rights reserved. PACS: 33.20.Lg; 33.20.Kf; 33.70.w Keywords: Organic materials; Electronic properties; Visible and ultraviolet spectra 1. Introduction Since the discovery of organic materials with conducting properties, organic optoelectronics has evolved into fields of fundamental and applied research leading to exciting sci- entific knowledge and many technological advances. The vision behind this studies is to design new organic materials for inexpensive applications, mainly as active elements in organic light-emitting diodes (LEDs), electroluminescence displays (ELDs), thin film transistors and photovoltaic devices. The advantages of organic LEDs and ELDs include low driving voltage, high brightness and wide viewing angles, in addition to their mechanical flexibility and extremely thin structure. However, some features are still expected to be improved, including colour gamut, luminance efficiency and device reliability, through increasing interest and research activities related to a recently newly designed and synthesized electronic organic materials. Among the number of such materials considerable interest represents pyrazolo- quinolines (1H-pyrazolo[3,4-b]quinoline and its deriva- tives). Recently they are found to be as a class of highly fluorescent materials in the blue spectral range [1] as well as promising materials for electroluminescent applications [2,3]. Our previous experiments and quantum chemical calculations on several pyrazoloquinoline derivatives have revealed their absorption spectra to be significantly 0030-4018/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2006.07.005 * Corresponding author. Tel.: +48 34 3250838; fax: +48 34 3250823. E-mail address: kityk@ap.univie.ac.at (A.V. Kityk). www.elsevier.com/locate/optcom Optics Communications 268 (2006) 64–74