Desenvolvimento de novos fluoróforos emissores no infravermelho baseados em sistemas híbridos moleculares doador-aceptor (D-A)

Abstract

The present Doctoral Thesis reports the synthesis, characterization and investigation of the photoluminescent properties of some new tailored design highly conjugated donor-acceptor (D-A) molecular hybrids for the development of more advanced and efficient Near-Infrared Fluorophores(NIRF). In the present work these novel fluorophores were obtained through condensation between two fluorescent molecular moieties: electron-donating aromatic amines (Ar2N) and electron-acceptoraromatic carboxylic unit (Ar1CO) in order to obtain the promising carboxamide Ar2N-COAr1 donoracceptor systems. Three acceptor (A, Ar1CO) moieties were investigated: beta-carboxy-thiophene(TfCO-), 3,4-imide-thiophene (Tf(CO)2) and squaric derivatives (SQCO-), and three donating fluorescent electrondonating amino-fluorene like subunits (D, Ar2N) were studied: (Ar = naphthyl, fluorene,dibenzofuran). Four novel beta-carboxamide thiophene molecular hybrid systems D-A (ThCO-NAr2) N-9Hfluoren-2-yl-3-thiophenecarboxyamide 5, N-3-dibenzofuranyl-3-thiophene, carboxyamide 6, N-2-naphtalenyl-3-thiophenecarboxyamide 7a and N-1-naphtalenyl-3-thiophenecarboxyamide 7b, were synthesized in good yields through the reaction between 3-thiophenecarbonyl chloride (4) and the aromatic amines 2-aminofluorene (1), 2-aminodibenzo furan (2), 2-naphthyl (3a), 1-naphthyl (3b). These four D-A binary molecular hybrids would be promising monomers to obtain the correspondingconducting homo-polymers (Poli-TfCO-NHAr)m, or a (D-A)m system. The direct electropolymerizations from the monomers 5-7, via cyclic voltammetry, were tried in order to prepare the correspondinghomopolymers using several conditions in the electrochemical medium, however, for none of these monomers the formation of films were observed. Nevertheless, the co-electropolymerization withEDOT (3,4-ethylenodioxithiophene) were possible to be performed by CV and the electrochemical profiles of the three copolymers PTfCO2Nft-co-PEDOT, PTfCO-2NFLU-co-PEDOT and PTfCO-2NDBZFco-PEDOT were determined by measurements of CV in comparison to the profile obtained for PEDOT and these data confirm that the copolymers present a remarkable gain in the electroactivity as wellpresented good thermal stability. The observation of the SEM images obtained for the films of copolymers corroborate the obtaining of the D-ADm molecular hybrids proposed in this work, sincethey present a quite synergism between PEDOT, electron-donor (D) unit and the aromatic carbonylamide-thiophenedonor-acceptor (DA)m moiety. The photophysical characteristics of the copolymers were investigated by ultraviolet-visible (UV-vis) absorption and fluorescence spectroscopyin dilute solutions of dimethylsulfoxide (=~ 10-8 g.L-1) and in the solid state. The emission close to infrared for the PTfCO2Nft-co-PEDOT (max=660 nm) is quite remarkable, but the NIR region emissions forPTfCO-2NFLU-co-PEDOT and PTfCO-2NDBZF-co-PEDOT, respectively at 706 and 710 nm. It is outstanding that quite intense NIR-emission (680-700 nm) of all studied films was also observed in solid state spectra, while PEDOT only emits at 648 nm. It is outstanding that these copolymers are indeed novel promising metal-free copolymeric NIR emitters. Two new N-aryl-3,4-thiophenedicarboximide or -3,4-thienopyrrolediones Ar2NCOTfOCNAr2 9 and 10 (Ar2 = 2-fluorenyl and 2-dibenzofuranyl), ternary molecular hybrids A-D-A were prepared through the condensation reaction between 3,4-dicarboxy-thiophene anhydride acceptor unit (8, A, 3,4-CO(O)Tf(CO), obtained from the dehydration of 3,4-dicarboxy thiophene (8.1)) and 2-fluorenyl 1 and 2-dibenzofuranyl amines 2. These novel imides present thermal stability until 250° C and the evaluation of the photoluminescence spectra might suggest the occurrence of charge transfer. It is noteworthy that both imides present maximum luminescence in very low concentrations of the order of 10-8 mol.L-1, N-fluorenyl-imide 9 shows maximum emission at 540 nm (yellow-green to yellow) and the dibenzofuran analog 10 has max emission at 575 nm (between yellow and orange red). Besides, the Raman spectrum performed at 1064 nm, Near Infrared (NIR) region, exhibits fluorescence for 9 and this fact needs to be further investigated. Theoretical calculations by DFT are still being made in order to get a better comprehension of the photophysical behavior of these imides. Nor the direct electropolymerization for homopolymers obtaining, nor the copolymerization with EDOT and even neither the chemical oxidative polymerization did not occur for these N-aryl-thiophene-imides.Two novel squaramide 2-naphthyl squaramides: mono-derivative mono-3-methoxy -4-(2-naphtalenylamino)-3-cyclobutene-1,2-dione (13, SQCO-Nft, a binary molecular hybrid D-A) and the bis-substituted squaramide bis-3,4-(2-naphtalenylamino)-3-cyclobutene-1,2-dione (14, a ternary molecular hybrid D-A-D) were synthesized, in good yields, via condensation reaction between the dimethylsquarate (12) and 2-naphthylamine (3a) in different molar ratios, and they were fullycharacterized by 13C-NMR, Raman and Infrared spectroscopy. The single-crystal X-ray crystallography for 13 crystal structures have been solved and the structure of 14 have been refined using PowderDiffraction state-of-art. Both squaramides present absorption in the ultra-visible (220-370 nm) and fluorescent emission in the NIR region (740-800 nm) and additionally they also presented high thermalstability (around 570 oC). Generally, only squaraines are reported as NIR emitters, this is the first description of NIR emission for squaramides, and since the synthesis of squaramides is very easy andthe rational design of small-molecule NIR fluorophores is of high priority these results are very promising for the development of novel NIR fluorescent dyes.