A series of novel heterocycle-based dyes with donor-pi-bridge-acceptor-pi-bridge-donor (D-pi-A-pi-D) structural motif, where benzothiazole serves as an electron-withdrawing core, have been designed and synthesized via palladium-catalyzed Sonogashira and Suzuki-type cross-coupling reactions. All the target chromophores show strong one-photon and two-photon excited emission. The maximum two-photon absorption (TPA) cross sections delta(TPA) of the prepared derivatives bearing diphenylamino functionalities occur at wavelengths ranging from 760 to 800 nm and are as large as approximately 900-1100 GM. One- and two-photon absorption characteristics of the title dyes have also been investigated by using density functional theory (DFT) and the structure-property relationships are discussed. The TPA cross sections calculated by means of quadratic response time-dependent DFT using the Coulomb-attenuated CAM-B3LYP functional support the experimentally observed trends within the series, as well as higher delta(TPA) values of the title compounds compared to those of analogous fluorene or carbazole-derived dyes. In contrast, the traditional B3LYP functional was not successful in predicting the observed trend of TPA cross sections for systems with different central cores. In general, structural modification of the pi-bridge composition by replacement of ethynylene (alkyne) with E-ethenylene (alkene) linkages and/or replacement of dialkylamino electron-donating edge substituents by diarylamino ones results in an increase of delta(TPA) values. The combination of large TPA cross sections and high emission quantum yields makes the title benzothiazole-based dyes attractive for applications involving two-photon excited fluorescence (TPEF).

Abstract:The synthesis and reactions of methyl 2-[3-(trifluoromethyl)phenyl]-4H-furo[3,2-b]pyrrole-5-carboxylate (1a) are described.Upon reaction with methyl iodide, benzyl chloride, or acetic anhydride, this compound gave N -substituted products 1b-d. By hydrolysis of compounds 1a-c, the corresponding acids 2a-c were formed, or by reaction with hydrazine-hydrate, the corresponding carbohydrazides 3a-c were formed. 5-[3-(trifluoromethyl)phenyl]furan-2-carboxaldehyde. The effect of microwave irradiation on some condensation reactions was compared with "classical" conditions. The results showed that microwave irradiation shortens the reaction time while affording comparable yields.

Keywords: methyl 2-[3-(trifluoromethyl)phenyl)]-4H-furo[3,2-b]pyrrole-5-carboxylate, 5-[3-(trifluoromethyl)phenyl]furan-2-carbaldehyde, 2-[3-(trifluoromethyl)phenyl)]furo[3,2-c]pyridine, Knoevenagel reaction.During the past few decades many results have been published in the field of synthesis and study of physical and chemical properties of heterocyclic compounds containing a furan ring connected or fused with a benzene ring or with different heterocyclic systems.Substituted furans are ubiquitous structural units in natural products and pharmaceuticals [1] and have been widely used as synthetic intermediates [2,3]. Many of the published condensation products are biologically active compounds [4,5] or can be used as intermediates in organic synthesis [6][7][8][9].In the past two decades one of us was interested in the syntheses, reaction, and aromaticity of variously substituted furo[3,2-b]pyrroles and their [2,3-b]-isomers [10,11]. Substitution, addition, and cycloaddition reactions of furo[3,2-b]pyrroles and their condensed derivatives involving the interesting transformations of furo[3,2-b]pyrrole system were presented. We also reported on the synthesis of 2-arylfuro[3,2-c]pyridines [12, 13] and 2,3-dimethylfuro[3,2-c]pyridine [14]. Later on some furo[3,2-c]pyridines have been used for the preparation of Cu(II) and Ni(II) complexes [15]. Furo[3,2-c]pyridine and its 2-methyl-, 2,3-dimethyl-and benzo [4,5] derivative were used for the first time as ligands to synthesize potentially new Werner clathrates, and the structural characterization, spectral, and magnetic properties of isothiocyanate nickel(II) complexes were published [16,17].

Eleven new 2-styrylbenzothiazole-N-oxides have been prepared by aldol – type condensation reactions between 2-methylbenzothiazole–N-oxide and para-substituted benzaldehydes. Compounds with cyclic amino substituents showed typical push-pull molecule properties. Four compounds were tested against various bacterial strains as well as the protozoan Euglena gracilis as model microorganisms. Unlike previously prepared analogous benzothiazolium salts, only weak activity was recorded.

Reactions of 5-[3-(Trifluoromethyl)phenyl]furan-2-carbaldehyde. -Knoevenagel condensation reactions of title compound (I) with compounds containing active methylene or methyl groups are performed and some of the new condensation products are transformed into fused aromatic heterocyclic systems containing the furan ring fused with pyrrole or pyridine ring. -(GAJDOS, P.; MIKLOVIC, J.; KRUTOSIKOVA*, A.; Chem. Heterocycl.