Optical properties of new pyrazolo[3,4-b]quinoline and its composites J. Niziol a,b,* , A. Danel c , G. Boiteux a , J. Davenas a , B. Jarosz c , A. Wisla c , G. Seytre a a Laboratoire des Materiaux Polymeres et Biomateriaux, UMR 5627, CNRSÐClaude Bernard Lyon 1 University, 43, bd. du 11 Novembre 1918, ISTIL, 69622 Villeurbanne, France b Faculty of Physics and Nuclear Techniques, University of Minning and Metallurgy, Al. Mickiewicza 30, 30-059 Krakow, Poland c Department of Chemistry, Hugon Kollataj Agricultural University, Al. Mickiewicza 24/28, 30-059 Krakow, Poland Abstract In this paper, new derivatives of pyrazolo[3,4-b]quinolines and their properties are reported. This materials, due to their high quantum ef®ciency of emission in the blue and the green, can be interesting for future application in electroluminescent devices. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Photoluminescence; Pyrazoloquinolines 1. Introduction Sincethelate1980s,light-emittingdiodesLEDs)basedon eithersmallorganicmoleculesOLED)orpolymersPLED) has been an object of big interest because of its numerous potentialapplication.Themainadvantageoforganicmateri- alsovertheirinorganiccompetitorsisthecheappriceandthe ease of different properties modi®cation. Although many compoundsemittingintheregionofgreenarealreadyknown, thereisstillimportantdemandformaterialshavinganintense emissionintheblueorintheredregionstoproducefull-colour RGB devices. Possible candidates for the blue emission are compounds from pyrazolo[3,4-b]quinoline PAQ) family, whichgeneralformulaispresentedinFig.1. The®rstpyrazolo[3,4-b]quinolinewaspreparedbyToma- sikandco-workers[1]in1928.Generalcharacteristicsofall sofarreportedPAQswastheiremissionintheblueandthe bluish-green.Thesecompoundswerealreadyinvestigatedas the active layers in electroluminescent devices [2]. In this paper,wereportpropertiesofaseriesofrecentlysynthesised new pyrazolo[3,4-b]quinoline derivatives. 2. Experimental 1. Synthesis details were similar to those described else- where [3]. The general structure of all prepared moleculeswaslikeinFig.1.Thenatureandthenumber of lateral groups are in Table 1. All these PAQs can be dividedinthreedistinctsets.ThefirstsetPAQ1±PAQ3) has lateral groups only at the positions 1 and 3. The second set has a phenyl group at the position 4. Molecules from the last set differ in donor/acceptor substitution in position 6 or 7. 2. Absorption and photoluminescence spectra were mea- sured both in solid-state and in solution. As the solution medium solvents of different dielectric constants were usedÐacetonitrile, chloroform, THF and cyclohexane. Solid-state spectra were measured on thin films evapo- ratedontoquartzglasssubstrates.Thequantumefficiency wasestimatedwithreferencetoquininesulphatein0.1M sulphuric acid. Thermal and crystallisation properties were investigated by DSC calorimetry, TGA in helium flow) and direct observations under a polarisation microscopethesamplewasplacedinahotstagecoupled with temperature and ramp controller). Thin blend films were prepared in PS matrix by spin-coating from the solutionofbothcompoundsinchloroform. 3. Results and discussion Both absorption and photoluminescence spectra are shown in Fig. 2. The absorption spectra of PAQs were intense and covered the entire ultraviolet zone and the blue endofthevisibleregion.Inspectraofallsamples,onecould easily distinguish the peak of HOMO to LUMO transition with its maximum ranging from about 380 to 420 nm, depending on the molecule. The molecules with donor or Synthetic Metals 127 2002) 175±180 * Corresponding author. Present address: Laboratoire des Materiaux Polymeres et Biomateriaux, UMR 5627, CNRSÐClaude Bernard Lyon 1 University, 43, bd. du 11 Novembre 1918, ISTIL, 69622 Villeurbanne, France. Fax: 33-47-889-2583. E-mail address: niziol@novell.ftj.agh.edu.pl J. Niziol). 0379-6779/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0379-677901)00617-8