Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Photoelectrical properties and surface examination of luminescent copolymer compounds G. Lewińska a, ⁎ , K.S. Danel b , A. Wisła-Świder b , Z. Usatenko c , J. Kanak a , Ł. Walczak d , P. Kuterba e , J. Sanetra, K.W. Marszalek a a AGH University of Science & Technology, Electronics Dept., 30 Mickiewicza Ave, 30-059 Krakow, Poland b University of Agriculture, Institute of Chemistry, Department of Food Technology, Balicka 122, 31-149 Kraków, Poland c Cracow University of Technology, Faculty of Materials Engineering and Physics , Institute of Physics, Podchorążych 1, 30-035 Krakow, Poland d R&D Department, PREVAC sp. z o.o., Raciborska 61, 44-362 Rogów, Poland e Jagiellonian University, Department of Physics, Astronomy and Applied Computer Science, Łojasiewicza 11, 30-348 Kraków, Poland ARTICLE INFO Keywords: OLED Copolymers Thin films Ellipsometry AFM ABSTRACT This work aimed to use copolymers in the production of organic light-emitting diodes, as well as to examine copolymers properties. Experimental optical absorption and fluorescence were determined, along with HOMO (the highest occupied molecular orbital) LUMO (the lowest unoccupied molecular orbital) levels. Refractive indexes and extinction coefficients were obtained using the ellipsometric spectroscopy method. Surface tests were performed using the atomic force microscope technique. The results of the molecular dynamics simulations are also presented. Light-emitting diodes were also produced, and their current-voltage and lighting-voltage characteristics were established. 1. Introduction Due to the growing demand for novel thin-film diode systems, new materials are being synthesised and investigated. Organic light- emitting diodes (OLEDs)[1] are being used in various applications, such as displays [2,3,4] and smartphones [5,6,7], among others [8,9,10]. The definite advantages of organic materials are their high brightness, fast responsiveness and wide viewing angle. Various chemical compounds, such as metal complexes, lanthanides, dis- tyrylarylene and oxadiazoles, are considered effective light emitters [11]. Furthermore, conjugated polymers are considered promising materials for OLEDs due to their high fluorescent efficiency com- bined with their mechanical flexibility [12]. This article presents the study of materials developed through the copolymerization of the new 1H-pyrazole [3,4-b] quinoline vinyl (PQ) with 9-vinylcarbazole. Due to its unique poly(N-vinylcarbazole) (PVK) properties [13,14,15] it is used as a functional polymer matrix for diodes. A photoexcited PVK molecule can transfer energy to an- other molecule. PVK is also a good hole transport material. Pyrazolopyridine derivatives are also materials of interest due to their optoelectronic properties. Pyrazolo-pyrimidine [16] or, to more be specific, pyrroloquinoline derivatives are applied in optoelectronic de- vices [17,18,19] as well as pharmaceutical applications [20]. The creation of such copolymers aims to combine the advantages of both components of the reaction. 2. Materials Four copolymer systems built from PVK and pyrazoloquinolines were examined, each at two different concentrations (eight compounds in total). In each of the compounds, pyrazoloquinolines accounted for either 0.1% or 1% of a given compound. These included 6-Methoxy-1,3- diphenyl-4-(4-vinyl-phenyl)-1H-pyrazolo [3,4-b] quinoline (PQ1); 1,3- diphenyl-4-vinyl-1H-pyrazolo [3,4-b] quinoline (PQ2); 4-(4-Fluoro- phenyl)-1,3-diphenyl-6-vinyl-1H-pyrazolo [3,4-b] quinoline (PQ3); and 1,3-diphenyl-6-vinyl-1H-pyrazolo [3,4-b] quinoline (PQ4). The procedures used to prepare the Me-PQ derivatives were as follows: the three-component (arylamine, aromatic aldehyde and pyr- azolone) reaction for PQ 1 [21] and PQ 3 , the Friedländer condensation of o-aminoacetophenone with pyrazolone for PQ 2 [22] and the con- densation between an aromatic amine and pyrazoloaldehyde for PQ 4 [23]. The methyl group was converted to the vinyl moiety using se- quential bromination of the methyl precursors, the reaction of the ha- lides with triphenylphosphine and the Wittig reaction with for- maldehyde [24]. Copolymers between N-vinylcarbazole and ethenyl- pyrazole-quinolines (PQ) were produced using radical polymerization https://doi.org/10.1016/j.apsusc.2020.147366 Received 19 May 2020; Received in revised form 17 July 2020; Accepted 25 July 2020 ⁎ Corresponding author. E-mail address: glewinska@agh.edu.pl (G. Lewińska). Applied Surface Science 533 (2020) 147366 Available online 08 August 2020 0169-4332/ © 2020 Elsevier B.V. All rights reserved. T