Materiais moleculares funcionais contendo n-heterociclos - capes

2856 R. Cristiano et al. / Tetrahedron 63 (2007) 2851–2858topography of the film of compound 15 is similar to that ofamorphous systems. This trend is in agreement with the differencesobserved in their luminescent and thermal properties.From the AFM images, we obtained the superficialroughness of the films, which is around 16 nm for 14 and7 nm for 15, indicating that the film of sample 15 is flatter.3. ConclusionsIn summary, a series of luminescent V-shaped low molecularmass materials containing a 2,3-dicyanopyrazine centralcore were synthesized and characterized. The photophysicaland thermal properties of these compounds, in solution andin solid state, were evaluated. These compounds displayedfluorescence in the solid state in a wide range of the spectra(from 430 to 512 nm). Most of the materials achieved goodthermal stability, exhibiting an amorphous glassy state aftermelting. Consequently, fluorescent transparent amorphousfilms can be easily obtained from these compounds by spincoating.4.1. General4. ExperimentalInfrared spectra were recorded on a Perkin–Elmer model283 spectrometer in KBr discs or films. 1 H NMR spectrawere obtained with a Varian Mercury Plus 400-MHz instrumentusing tetramethylsilane (TMS) as the internal standard.13 C NMR spectra were recorded on a Varian Mercury Plus100-MHz spectrometer. Elemental analyses were carriedout using a Perkin–Elmer model 2400 instrument. Lowresolutionmass spectra were recorded on a triple quadrupolemass spectrometer, GCMS-QP5050A Shimadzu. The meltingpoints, thermal transitions, and mesomorphic textureswere determined using an Olympus BX50 microscopeequipped with a Mettler Toledo FP-82 hot stage and a PM-30 exposure control unit. DSC measurements were carriedout using Shimadzu equipment with a DSC-50 module. AnHP UV–Vis model 8453 spectrophotometer was used torecord absorption spectra. Fluorescence spectra were recordedon a Hitachi-F-4500. The relative quantum yieldsof fluorescence (F F ) for all compounds are determinedaccording to Eq. 1:F unk ¼ F std ðI unk =A unk ÞðA std =I std Þðh std =h unk Þ 2ð1Þwhere F std is the fluorescence yield of standard quinine sulfate(F std ¼0.546 in 1 M H 2 SO 4 at 298 K); I unk and I std arethe integrated emission intensities of the sample and standard,respectively; A unk and A std are the absorbance of thesample and standard, respectively, at the desired wavelengthl exc (380 nm) such that absorbances were less than 0.10; andh unk and h std are the refractive indexes of the sample andstandard solutions.4.2. MaterialsAll the reagents were obtained from commercial sourcesand used without further purification. In general, all thecompounds were purified by column chromatography on silicagel (70–230 mesh), and crystallization from analyticalgrade solvents. Carboxylic acids 1, 2, 3, and 4 were preparedaccording to published procedures. 15–18 4 0 -(3,4,5-Tridodecyloxybenzoyloxy)benzoicacid 5 was obtained from theiterative esterification of 3,4,5-tridodecyloxybenzoic acid2 with benzyl-4-hydroxybenzoate followed by deprotectionof the benzyl ester through a modified version of a proceduregiven in the literature. 19 Acid 6 was synthesized throughWilliamson etherification of methyl 3,4,5-trihydroxybenzoatewith 4-n-dodecyloxybenzyl bromide, followed byalkaline ester cleavage according to a method described indetail elsewhere. 20 Anisil 7 was synthesized through benzoincondensation of anisaldehyde 21 followed by hydroxyloxidation using copper(II) sulfate/pyridine. 22 Compound9 was synthesized according to a procedure given in theliterature. 224.3. X-ray crystallographic analysisSuitable crystals of 8 were obtained through recrystallizationfrom methanol followed by filtration of the crystals andwashing with cold methanol. Crystallographic analysiswas carried out at room temperature with a selected prismaticyellow crystal, which was mounted on a CAD-4Enraf–Nonius diffractometer using graphite monochromatedMo Ka radiation (l¼0.71073 Å). Cell parameters weredetermined from 25 centered reflections in the q range of4.96 –16.99 . Intensities of 3130 were collected using theu 2q scan technique with a q angle ranging from 1.65 to25.07 . The structure was solved using direct methodswith SIR-97 23 and refined by full-matrix least-squares procedureson F 2 using SHELXL-97. 24 H atoms bonded to Catoms were added at their calculated positions and includedin the structure factor calculations, with C–H distances andU eq taken from the default of the refinement program.Selected crystal data: C 20 H 14 N 4 O 2 , M¼342.35, monoclinic,P2 1 /n, a¼9.498(1) Å, b¼7.38(1) Å, c¼24.664(2) Å, b¼93.72(1) , V¼1726.0(3) Å 3 , Z¼4, D calcd ¼1.317 Mg/m 3 ,m¼0.089 mm 1 , F(000)¼712, unique 3056 (R int ¼0.0147),refined parameters¼237, Goof (F 2 )¼1.032, R 1 [I>2s(I)]¼0.0422, wR 2 (all data)¼0.1207.Crystallographic data (excluding structure factors) for thestructure reported in this paper have been deposited at theCambridge Crystallographic Data Centre under supplementarypublication number CCDC 623033. Copies of the datacan be obtained, free of charge, on application to CCDC,12 Union Road, Cambridge, CB2 1EZ, UK [fax: +44(0)1223 336033, e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk)].4.4. Film preparation and characterizationThe films were deposited on quartz plates for the opticalabsorption and emission measurements. Before deposition,the plates were first carefully cleaned by washing withneutral detergent and then, followed by a sequence of20-min sonications in acetone, alcohol, and water, andfinally dried in an oven. The studied compounds weredissolved in chloroform, at 2% (wt), and then depositedby spin coating at 4000 rpm for 30 s, at room temperature(24 C).