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The four empirical solvent polarity parameters according to the Catalán scale--solvent acidity (SA), solvent basicity (SB), solvent polarizability (SP), and solvent dipolarity (SdP)--of 64 ionic liquids (ILs) were determined by the solvatochromic method. The SA parameter was determined solely by using [Fe(II)(1,10-phenanthroline)2(CN)2] (Fe), the SB parameter by using the pair of structurally comparable dyes 3-(4-amino-3-methylphenyl)-7-phenylbenzo[1,2-b:4,5-b']difuran-2,6-dione (ABF) and 3-(4-N,N-dimethylaminophenyl)-7-phenylbenzo[1,2-b:4,5-b']-difuran-2,6-dione (DMe-ABF), and the SP and SdP parameters by using the homomorphic pair of 4-tert-butyl-2-(dicyanomethylene)-5-[4-(diethylamino)benzylidene]-Δ(3)-thiazoline (Th) and 2-[4-(N,N-dimethylamino)benzylidene]malononitrile (BMN). The separation of SP and SdP for a set of 64 various ILs was performed for the first time. Correlation analyses of SP with physicochemical data related to ionization potentials of anions of ILs as well as with theoretical data show the correctness of the applied method. The found correlations of the Catalán parameters with each other and with the alkyl-chain length of 1-alkyl-3-methylimidazolium-type ILs gives new information about interactions within ILs. An analytical comparison of the determined Catalán parameters with the established Kamlet-Taft parameters and the Gutmann acceptor and donor numbers is also presented.

The specific barbituric acid dyes 1-n-butyl-5-(2,4-dinitro-phenyl) barbituric acid and 1-n-butyl-5-{4-[(1,3-dioxo-1H-inden-(3 H)-ylidene)methyl]phenyl}barbituric acid were used to study complex formation with nucleobase derivatives and related model compounds. The enol form of both compounds shows a strong bathochromic shift of the UV/Vis absorption band compared to the rarely coloured keto form. The keto-enol equilibria of the five studied dyes are strongly dependent on the properties of the environment as shown by solvatochromic studies in ionic liquids and a set of organic solvents. Enol form development of the barbituric acid dyes is also associated with alteration of the hydrogen bonding pattern from the ADA to the DDA type (A=hydrogen bond acceptor site, D=donor site). Receptor-induced altering of ADA towards DDA hydrogen bonding patterns of the chromophores are utilised to study supramolecular complex formation. As complementary receptors 9-ethyladenine, 1-n-butylcytosine, 1-n-butylthymine, 9-ethylguanidine and 2,6-diacetamidopiridine were used. The UV/Vis spectroscopic response of acid-base reaction compared to supramolecular complex formation is evaluated by (1)H NMR titration experiments and X-ray crystal structure analyses. An increased acidity of the barbituric acid derivative promotes genuine salt formation. In contrast, supramolecular complex formation is preferred for the weaker acidic barbituric acid.

A series of 3,4-di-N-substituted 2,5-diferrocenyl thiophenes is reported with the aim to explore the electronic interaction between the organometallic termini over their bridging unit. The syntheses of thiophenes 1−4 were implemented on the basis of 2,5-diferrocenyl-3,4-dinitrothiophene (1), which is accessible within a Pd-promoted Suzuki− Miyaura C,C cross-coupling reaction. Reduction of the nitro functionalities and a subsequent methylation or condensation reaction gives 2,5-diferrocenyl-3,4-bis(N, (4) could be synthesized through conversion of 3 in a two-step reduction/methylation reaction. The spectroscopic characterization of 1−4 was complemented by the investigation of their structural properties in the solid state. The latter disclose no significant influence of the electronically different N substituents on the thiophene bond distances and angles in the solid state. UV−vis solvatochromic studies on thiophenes 1 and 3 in 40 different solvents offer a moderate positive solvatochromic shift of the MLCT absorption of 1; however, for pyrazine 3 a slight negative solvatochromism of the appropriate absorption band was observed. The electrochemical studies on thiophenes 1−4 reveal an increasing thermodynamic stability of the mixed-valent species (K C ) in the order 1 < 2 ≈ 3 < 4. In situ UV−vis−NIR spectroelectrochemical examinations verify these observations. Thus, the NIR absorptions of the corresponding mixed-valent species become more intense and less solvatochromic as the electron-donating effect and the extent of the electronic π system of the bridging unit increase. Hence, the electronic coupling between the iron-based redox centers over the thiophene-based core increases in the order 1 < 2 ≈ 3 < 4.

Pd-catalyzed amination polymerization of deep blue aminobenzodifuranone monomer 3-(4-bromo-phenyl)-7-(4-octylaminophenyl)-benzo[1,2-b:4,5-b 0 ]-difuran-2,6-dione (M1) is described, as well as polymerization of symmetric dibromophenyl-benzodifuranone (M2), or the corresponding dibromophenylbenzodipyrrolidone (M3) with N,N 0 -dialkylated phenylenediamines (M4a,b). The resulting polymers P1-3 exhibit low bandgaps (1.08-1.47 eV), broad UV/vis absorption bands (400-900 nm), and a large solvatochromic shift up to 3140 cm À1 from n-hexane to hexamethylphosphoramide. Multiple linear regression analyses ofñ max of the solvent-dependent solvatochromic UV/vis absorption bands of M1, P1 and P2a are presented, from which Kamlet-Taft and Catalán solvent parameters were determined. All monomers and polymers exhibit high extinction coefficients up to 8.6 Â 10 4 L mol À1 cm À1 and high photostability, and might be suitable for electronic applications. † Electronic supplementary information (ESI) available: Experimental details, the 1 H NMR spectrum of 4-(octyl amino)phenyl tartronic acid, UV/vis absorption spectra of M2 and M3 and polymers P1, P2a and P3, before and aer irradiation in toluene, and solvatochromic data. See Scheme 2 Synthesis and structure of polymers P1-3. (i) Pd 2 (dba) 3 , X-Phos, Cs 2 CO 3 (t-BuOK for P3), DMF-toluene (2/1) (dioxane for P1 and P3), N 2 .Scheme 1 Synthesis and structure of M1.This journal is