Abstract:
SBF derivatives, represented with the following formula: SBF-X wherein: 
                                 
with
   m=0, 1, 2 or 3;   p=positive integer,;   n=positive integer;   L: is the same or different and independently represents C, PR, AsR, SbR, BiR, S, Se, Te, S═Y, Se═Y or Te═Y;   Y: is the same or different and independently represents O, S, Se or Te; K: is the same or different and independently represents a chemical bond or a group selected from O, S, BR (2−p) , N, NR (2−p) , R (2−p) P═O, B 3 O 3 , (PR) 3 N 3 , CR (3−p) , CR (3−p) (C 6 H 4 ) (p+1) , SiR (3−p) (C 6 H 4 ) (p+1)  alkyne, substituted alkyne, alkyne, substituted alkyne, aromatic or R substituted aromatic, heteroaromatic-or a combination of two, three or four of the above mentioned groups; SBF: spiro-compound of formula (I):   
 
     
       
                 
         
             
             
         
       
       
         R, A, B, C, D: is the same or different and independently represents H, deuterium, F, Cl, Br, I, CN, a linear, branched or cyclic alkyl, alkoxy or thioalkoxy chain, or a combination from two, three or four of these systems; two or more substituents R can form a further monocyclic or polycyclic aliphatic or aromatic ring system with each other.

Description:
RELATED APPLICATIONS 
     This application is a national stage application (under 35 U.S.C. 371) of PCT/EP2005/007746 filed Jul. 15, 2005, which claims the benefit of Italian application RM2004A000352 filed Jul. 15, 2004. 
     FIELD OF THE INVENTION 
     The present invention relates to oligomeric derivatives of spirobifluorene of general formula SBF-X, wherein the SBF group and the X term are specified below. The invention also relates to the synthesis method of said compounds and their use, in particular their use as materials in the field of molecular electronics. 
     KNOWN ART 
     Spirobifluorenes (SBF) are a class of spiro-compounds well known in organic chemistry, [(9,9′-spirobi[9H-fluorene])]. Their molecular structure is composed of two identical halves, each one of conjugated aromatic type, bond together by a quaternary sp 3  carbon atom. The consequences of these features are: the two halves of the molecule are in mutually perpendicular; said two halves cannot be considered conjugated to each other in the classical meaning of the term. 
     The preparation of these compounds is described by Prelog (1) and their application features are described in Aviram (2), as well as in EP 0676461. 
     SBFs are among those classes of organic molecules which can be used in the arrangement and realization of electronic circuits and switches for organic electronic devices. 
     SBF derivatives are described in WO 04/013080, however these compounds are not all satisfactory for the applications which include blue light OLEDs as well as OLEDs emitting light from the triplet excited state. 
     US 2003/0065190 discloses some SBF derivatives to be used, for example, as electroluminescence materials; however these compounds are not all satisfactory with respect to the solubility features in common organic solvents, the electron acceptance of one or more electrons and the molecular symmetry, properties which are considered to be advantageous for the uses described below. 
     The inventors have now found a class of compounds, SBF derivatives, which exhibits particularly interesting physical-chemical features with respect to the known art for the use in the field of molecular electronics, especially in OLEDs, with the general term of molecular electronics meaning the technical field for which organic molecular species can be used for electronic applications (3) (the electroluminescence and the photoluminescence are techniques included in this expression). Further, these compounds can be of use as electron transport materials in OLEDs as well as in other applications. They can be further used as matrix materials for emitters, emitting light from the triplet excited state. 
     SUMMARY OF THE INVENTION 
     Object of the present invention are therefore the SBF (spirobifluorene) derivatives, which can be represented by the following formula: SBF-X, wherein: 
                                
with
     m=0, 1, 2 or 3;   p=positive integer, preferably 1, 2 or 3, with (p+1) being the valency of K;   n=positive integer, preferably 1, 2, 3 or 4;   L: is the same or different and independently represents C, PR, AsR, SbR, BiR, S, Se, Te, S═Y, Se═Y or Te═Y;   Y: is the same or different and independently represents O, S, Se or Te;   K: is the same or different and independently represents a chemical bond or a group selected from O, S, BR (2−p) , N, NR (2−p) , R (2−p) P═O, B 3 O 3 , (PR) 3 N 3 , CR (3−p) , CR (3−p) (C 6 H 4 ) (p+1) , SiR (3−p) (C 6 H 4 ) (p+1)  with (2−p) and (3−p) being a positive integer including zero; alkane, substituted alkane, alkene, substituted alkene, alkyne, substituted alkyne, aromatic or R substituted aromatic, heteroaromatic or R substituted heteroaromatic or a group originating from benzene and non benzene, monocyclic and polycyclic hydrocarbons which can be bivalent, trivalent or of higher valency; or a combination of two, three or four of the above mentioned groups;
 
SBF: spiro-compound of formula (I):
   

                                
R, A, B, C, D: is the same or different and independently represents H, deuterium, F, Cl, Br, I, CN, a linear, branched or cyclic alkyl, alkoxy or thioalkoxy chain with 1 to 40 carbon atoms, which can be substituted by R 1  and in which one or more non-neighbouring carbon atoms can be replaced by N—R 1 , O, S, C═O, C═S, C═NR 1 , Si(R 1 ) 2 , Ge(R 1 ) 2 , O—CO—O, CO—O, CO—NR 1 , —CR 1 ═CR 1 — or —C≡C— and in which one or more H-atoms can be replaced by F, Cl, Br, I or CN, or an aromatic or heteroaromatic ring system with 5 to 40 aromatic ring atoms, which can be substituted by deuterium, F, Cl, Br, I, CN or one or more substituents R 1 , or a combination from two, three or four of these systems; two or more substituents R can form a further monocyclic or polycyclic aliphatic or aromatic ring system with each other;
 
R 1 : is the same or different and independently represents H or an aliphatic or aromatic hydrocarbon rest with 1 to 20 C-atoms; wherein the following compounds are excluded:
 
                                
wherein L, A, B, C and D have the same meaning as above and Ar is the same or different from one another and independently represents a bivalent aromatic or heteroaromatic ring system with 2 to 40 carbon atoms, wherein one or more hydrogen atoms can be replaced by F, Cl, Br or I and which can be substituted by one or more non-aromatic substituents R; two or more substituents R, A, B, C or D on the same ring as well as on different rings, can form a further monocyclic or polycyclic aliphatic or aromatic ring system with each other.
 
     By way of example, the K group coming from benzene and non-benzene, monocyclic and polycyclic hydrocarbons, is preferably selected among: benzene, naphthalene, anthracene, naphthacene, pyrene, perylene, phenanthrene, chrysene, fluoranthene, triphenylene, azulene, 1,1′-biazulene, biphenyl, triphenylamine, triphenylphosphine, triazine, 1,3,5-triphenylbenzene, 1,3,5-triphenyltriazine, furane, thiophene, pyrrole, 1,3,4-oxadiazole, 1,3,4-thiadiazole, diphenyloxadiazole, oxazole, thioazole, aromatic anhydrides, aromatic dianhydrides or adamantane and derivatives. In addition, K can be selected resulting from the following products which each can be substituted by a group R or unsubstituted (each compound being identified in the order from: name, CAS number or bibliographic ref. where known, acronym): 
     
       
                 
         
             
             
         
      
       
                 
         
             
             
         
       
     
     In a preferred embodiment of the invention, L is the same or different and independently represents C, PR, S or S═Y, particularly preferred C or PR, very particularly preferred C. 
     In a further preferred embodiment of the invention, Y is the same or different and independently represents O or S, particularly O. 
     Another object of the invention are the radical anions corresponding to compounds of formula SBF-X. By radical anion is meant the chemical species obtained by addition of one electron to the corresponding neutral species. In the compounds of the present invention, the molecule can gain more than one electron. 
     Still another object of the invention is a method for preparing the compounds according to the invention and a method for preparing the corresponding radical anions. 
     Another object of the invention are radical cations corresponding to compounds of formula SBF-X. By radical cation is meant the chemical species obtained by loss of one electron from the corresponding neutral species. 
     Still another object of the invention are organic electronic devices, OLEDs (organic light emitting diodes), particularly the blue OLEDs and OLEDs emitting light from the triplet state, organic field effect transistors, organic lasers, organic field quenching devices, organic phototransistors, organic photochromic materials, organic solar cells, and components for non linear optics using the compounds according to the invention or the corresponding radical anions. 
     Further objects of the invention will result apparent from the detailed description of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to compounds of formula SBF-X, as above-specified, to spiro-compounds, wherein at least two SBF groups are connected together through at least a carbonyl group (C═O) and to corresponding derivatives. According to the present invention, by the term derivatives are intended those obtainable according to the classical organic procedure, included therein the corresponding salts, for example as described in (4). 
     Preferred compounds according to the invention are:
         those having more than one L=Y group, wherein said L=Y groups are conjugated with SBF;   those wherein K is alkene or alkyne and n=1;   those wherein K is phenyl or substituted phenyl and p=2;   those wherein K is naphthalene or substituted naphthalene or pyrene or substituted pyrene and p=3;   those wherein K is phenyl, biphenyl, 1-naphthyl, 2-naphthyl, 2-thienyl, 2-furyl, 2-pyrrole.       

     Within the scope of the present invention and referring to the general formula, particularly preferred are the following compounds: 
     
       
                 
         
             
             
         
      
     
     Since some of the molecules of the invention present axial asymmetry, the enantiomers both in a mixture and as pure compounds are included within the scope of the invention. 
     The compounds of the invention can be prepared starting from commercially available or easily producible compounds according to the classical reactions known to the skilled in the art (4), (8), for example starting from corresponding acyl halides, preferably acid chlorides, through Friedel-Crafts reaction (8). If said acid halides are not commercially available, it is possible to start from the corresponding carboxylic acids in the following manner: to a solution containing a certain quantity of carboxylic acid dissolved in thionyl chloride, a few drops of N,N′-dimethylformamide are added, then the solution is heated under reflux for some hours; after cooling at room temperature, the excess thionyl chloride is removed under reduced pressure, then petroleum ether is added and a vacuum distillation is executed to obtain the corresponding acid chloride. 
     The following SBF bonding occurs with the conventional methods, as above-mentioned. 
     As above-mentioned, a method for preparing the compounds of the invention involves the Friedel-Crafts acylation (8) of SBF, using aluminum chloride AlCl 3  as a catalyst or another analogous catalyst and includes the following stages:
         select the acyl halide depending on the final compound to be obtained and place it in a solvent, preferably dichloromethane, at a temperature not above 15-20° C., preferably in a water/ice bath;   add SBF, if necessary functionalized, preferably dropwise and under stirring, and heat under reflux to complete the reaction;   take up the final compound by adding to the reaction mixture a diluted aqueous solution of a mineral acid, preferably HCl;   separate the organic phase and repeat the extraction operation, collecting all the organic extracts in which the final product is contained, obtainable through conventional techniques, such as crystallization or solvent evaporation.       

     The optimal conditions for obtaining the desired compounds are within the reach of the skilled in the art. 
     In case of intermediates (II) to (IX), it is possible to start from the SBF acid chloride. 
     The anionic radicals of the compounds of the invention are preferably obtained by chemical or electrochemical way with the addition of an electron to the corresponding neutral compound; the electrochemical way is particularly preferred because of its selectivity and easiness of execution. 
     For obtaining dianionic diradicals, when it is possible, which can be paramagnetic species, it is enough to operate at more negative potentials with respect to those relating to the radical anions, shown by the experimental conditions. 
     An example of radical anions is given in the experimental part in example 6. 
     The electrochemical method for obtaining the radical anions is generally described in (5) and (6). Such method is carried out by using an electrochemical cell having two compartments: an anodic one and a cathodic one; in the cathodic one a working electrode and a reference calomel electrode are placed. An aprotic solvent or mixtures of typically N,N-dimethylformamide, acetonitrile, tetrahydrofuran, N-methyl-pyrrolidone, dimethylsulfoxide, preferably N,N-dimethylformamide, acetonitrile and, particularly preferably N,N-dimethylformamide, is made anhydrous according to the usual procedures (5), to this a support electrolyte is added, typically tetraethylammonium perchlorate, tetrabutylammonium tetrafluoroborate, lithium perchlorate, particularly preferably tetraethylammonium perchlorate, which is made anhydrous as well, so as to obtain a concentration between 1 M and 0.01 M, preferably 0.2M and 0.05M, with particular preference about 0.1M. 
     The electrolytic solution thus prepared is placed in the cathodic compartment which is separated from the anodic one through a portion of the same electrolytic solution, properly gelled, and in which the anode is present (Pt net). 
     The selected compound is added to the electrolyte solution present in the cathodic compartment of a divided cell, under a nitrogen flow, in such a way to obtain a concentration between 0.01 M and 0.1 mM, preferably between 0.01 M and 0.5 mM and with particular preference 1 mM. In the cathodic compartment of the cell a reticulated vitreous carbon (RVC) electrode, as a cathode, and a calomel electrode (SCE) as a reference electrode are placed. In the anodic compartment of the cell, which is divided from the cathodic compartment by means of a gelled electrolyte solution, a preferably platinum-net electrode is placed as an anode. Other electrode materials usable as working electrode are: mercury, lead, silver, Ti-based composite materials, conductive carbon materials, carbon-containing conductive materials, chemically modified electrodes, particularly preferred is the glassy carbon for the following features: wide applicable d.d.p. window, inexpensiveness, non toxicity and easiness of use. 
     The usable carrier electrolytes are those preferably containing: perchlorate anions, tetrafluoroborate anions, hexafluorophosphate anions, lithium cations, sodium cations, tetraalkylammonium cations and respective mixtures; particularly preferred are perchlorate anions and tetraethylammonium cations. 
     Between the electrodes a proper d.d.p. is applied, so as to obtain the desired radical anion, generally a d.d.p. of about 0.2 V more negative than the standard potential E° of the compound to be treated (vs SCE). 
     The working temperatures can be between −20° C. and +50° C.; particularly preferred is room temperature. 
     The compounds of the invention, due to the presence of the C═O group/s interposed between the SBF groups, form more easily the radical anions with respect to the corresponding compounds wherein C═O is not present. 
     In fact, it has been observed that the introduction of the functional conjugated C═O group has, as a consequence, a remarkable improvement of the molecule property, because it confers thereto an increase in the “electron acceptor” feature, by shifting the standard potential, E°, of the molecule towards more positive (lower) values. It is known that the standard potential, E°, defined as in (6), shifts towards more positive values with respect to a reference molecule when its properties as electron-acceptor are improved based on the reference molecule. 
     Referring to the compounds, corresponding derivatives and salts according to the present invention and to corresponding radical anions, the standard potential E° shifts towards more positive values of the ΔE° quantity. The ΔE° increment towards more positive potentials with respect to values of corresponding compounds without the functional C═O group has the advantage that the uses of the molecule of the invention involve an energy saving. The compounds of the invention and the corresponding radical anions, due to the presence of a plurality of conjugated C═O groups, can be generally advantageously employed in the electroluminescence field, particularly for light-emitting diodes (OLEDs), more particularly blue-light OLEDs and OLEDs emitting from the triplet state, as electron transporting materials in OLEDs as well as in other applications, as molecular switching components, for non linear optics, in molecular-based computational systems (this latter described in Aviram, ref. (1)), in field-effect transistors (FET) (7), in negative differential resistance (NDR) semiconductors. Just for the presence of many conjugated C═O groups, the compounds of the invention allow the easy transfer of more electrons with respect to similar compounds, thus allowing to obtain anionic species usable as molecular magnets. 
     The compounds of the invention, preferably in the enantiomeric form, can be used for applications in molecular biology and in nanotechnologies related to this latter. The compounds according to the invention can be applied in form of thin film or coating upon a proper substrate (metallic or non metallic) according to techniques (for example chemical, physical-chemical, physical) known to those skilled in the art. The devices carry at least an active layer including at least one compound of the invention, applied on said substrate. 
     The organic electronic device is preferably selected from the group consisting of organic and polymeric light emitting diodes (OLEDs, PLEDs), organic field-effect transistors (O-FETs), organic thin film transistors (O-TFTs), organic light emitting transistors (O-LETs), organic integrated circuits (O-ICs), organic solar cells (O-SCs), organic field quench devices (O-FQDs) or organic laser diodes (O-Laser). Particularly preferred are organic or polymeric light emitting diodes. 
     The compounds can be applied on the substrate of the organic electronic device by sublimation, preferably at a pressure below 10 −5  mbar, more preferably below 10 −6  mbar, most preferably below 10 −7  mbar. 
     The compounds can further be applied on the substrate of the organic electronic device by the OVPD (organic vapour phase deposition) process or by means of a train sublimation. The materials are applied with these methods at a pressure between 10 −5  mbar and 1 bar. 
     The compounds can further be applied on the substrate of the organic electronic device from solution, e.g. by spin-coating, or by a printing method, such as offset-printing, or preferably by LITI (light induced thermal imaging) order by ink-jet printing. 
     The following examples are given by way of illustration of the invention and are not to be considered limiting of the same. 
     EXAMPLES 
     Reagents and instruments: carbon sulfide (CS 2 ) Carlo Erba; aluminum trichloride (AlCl 3 ) Fluka; thionyl chloride (SOCl 2 ) Merck; IR: Perkin-Elmer 298, Shimadzu 470; NMR; Bruker AC 200. All the acid chlorides used are Aldrich, 2-bromobiphenyl and truxenone are Lancaster products. 
     Example 1 
     Preparation of SBF (COC═CCO) SBF (SBF-fumaryl ketone) (X) 
     To 110 mg fumaryl chloride (d=1.413 g/ml; 0.08 ml) in 20 ml CH 2 Cl 2 , 210 mg of finely pulverized anhydrous AlCl 3  is added at 15° C. (water-ice bath) (black colour). A solution containing 500 mg 9,9′-spirobifluorene in 20 ml CH 2 Cl 2  is added dropwise under stirring within 30 minutes and is allowed to reach RT (room temperature) (red-blue colour). Then, the mixture is heated under reflux and the stirring is maintained for two more hours. After treatment with water and ice and then with diluted HCl, the organic phase is separated (orange colour). The organic extracts are treated with saturated sodium carbonate, washed with water and dried on anhydrous sodium sulphate. Column chromatography, eluent 25% ethyl acetate/hexane (plate at 30% with the same eluents). 
       13 C-NMR (CDCl 3 , 50 MHz, δ [ppm] vs SiMe 4 ): 191.6 (CO), 150.2, 149.3, 147.6, 146.9, 141.8, 140.3, 135.7, (all quaternary carbon atoms); 135.2, 129.2, 127.9, 124.2, 123.9, 120.9, 120.0, 119.8 (all CH); 65.6 (C-spiro). 
     Example 2 
     Preparation of Ph(1.3-CO-SBF) 2  (1,3-DICO) (XI) 
     
       
                 
         
             
             
         
      
     
     To 353 mg isophthaloyl chloride (1.74 mmols) in 20 ml CH 2 Cl 2 , 232 mg of finely pulverized anhydrous AlCl 3  (1.74 mmols) is added at 15° C. (water-ice bath) (yellow colour). A solution containing 250 mg 9,9′-spirobifluorene (0.79 mmols) in 10 ml CH 2 Cl 2  is added dropwise and under stirring within 30 minutes and is allowed to reach RT (red colour). Then, the mixture is heated under reflux and the stirring is maintained for two more hours. After treatment with water and ice and then with diluted HCl the organic phase is separated (white colour). The organic extracts are treated with saturated sodium carbonate, washed with water and dried on anhydrous sodium sulphate. Column chromatography, eluent 40% CH 2 Cl 2 /hexane (plate at 60% with the same eluents). 
       1 H-NMR (CDCl 3 , 200 MHz, δ [ppm] vs SiMe 4 ): 7.62-8.22 (34 H, mc, ArH) 
       13 C-NMR (CDCl 3 , 50 MHz, δ [ppm] vs SiMe 4 ): 193.6 (CO), 65.8 (spiro C). 
     Example 3 
     Preparation of Ph(1.4-CO-SBF) 2  (1,4-DICO) (XII) 
     
       
                 
         
             
             
         
      
     
     To 353 mg terephthaloyl chloride (1.74 mmols) in 20 ml CH 2 Cl 2 , 232 mg of finely pulverized anhydrous AlCl 3  (1.74 mmols) are added at 15° C. (water-ice bath) (yellow colour). A solution containing 250 mg 9,9′-spirobifluorene (0.79 mmols) is added dropwise in 10 ml CH 2 Cl 2  and under stirring within 30 minutes and is allowed to reach RT (red colour). Then, the mixture is heated under reflux and the stirring is maintained for two more hours. After treatment with water and ice and then with diluted HCl the organic phase is separated (white colour). The organic extracts are treated with saturated sodium carbonate, washed with water and dried on anhydrous sodium sulphate. Column chromatography, eluent 40% CH 2 Cl 2 -hexane (plate at 60% with the same eluents). 
       1 H-NMR (CDCl 3 , 200 MHz, δ [ppm] vs SiMe 4 ): 6.82-8.22 (34 H, mc, ArH) 
       13 C-NMR (CDCl 3 , 50 MHz, δ [ppm] vs SiMe 4 ): 195.2 (CO), 65.8 (spiro C). 
     Example 4 
     Preparation of Ph(CO-SBF) 3  (TRICO) (XIII) 
     To 1.26 g 1,3,5-benzenetricarbonyl trichloride (4.74 mmols) in 20 ml CH 2 Cl 2 , 843 mg of finely pulverized anhydrous AlCl 3  (6.32 mmols) is added at 15° C. (water-ice bath) (yellow colour). A solution containing 500 mg 9,9′-spirobifluorene (1.58 mmols) in 10 ml CH 2 Cl 2  is added dropwise and under stirring within 30 minutes and is allowed to reach RT (green-orange-red colour). Then, the mixture is heated under reflux and the stirring is maintained for two more hours. After treatment with water and ice and then with diluted HCl the organic phase is separated. The organic extracts are treated with saturated sodium carbonate, washed with water and dried on anhydrous sodium sulphate; a yellow waxy liquid is obtained. Column chromatography, eluent 40% CH 2 Cl 2 -hexane (plate at 60% with the same eluents). 
       13 C-NMR (CDCl 3 , 50 MHz, δ [ppm] vs SiMe 4 ): 191.5 (CO), 65.6 (spiro C). 
     Example 5 
     Preparation of Tri-Spirobifluorene (Spirotruxene) (VIII) 
     To a solution of 2-bromobiphenyl (14.3 mmols; 0.9 g; 2.4 ml) dissolved in 20 ml anhydrous THF is added at −78° C. n-BuLi (32.5 mmol; 2.5 M in hexane; 13 ml) within 30 minutes, then it is brought to 0° C. By means of a syringe, the lithiated compound is transferred in a dropping funnel of a second flask wherein a Truxenone suspension is contained (1.3 mmol; 0.5 g) dissolved in 30 ml anhydrous THF, and is slowly added at 0° C. The solution is brought at room temperature, maintained at this temperature for 4 h and then treated with a saturated solution of NH 4 Cl. The aqueous solution is extracted with CH 2 Cl 2  (3×15 ml), the organic phases are dried over anhydrous sodium sulphate. After vacuum evaporation of the solvent a reddish liquid is obtained, isomers mixture. The liquid is dissolved in 10 ml of glacial acetic acid and the mixture is heated under reflux, then a few drops of conc. HCl are added and it is refluxed for one more minute. Then, water is added until turbidity, it is allowed to cool, filtered over Gooch. The acid aqueous phase is extracted with CH 2 Cl 2  and dried over anhydrous sodium sulphate, then it is dried in the rotavapor. A beige precipitate is obtained insoluble in the common solvents (850 mg). From the NMR spectrum of the precipitate in DMSO it results to be the Spirotruxene (yield of 78%). 
     Spirotruxene (VII): 
       1 H-NMR (DMSO, 200 MHz): 7.62-7.27 (36 H, m, ArH). 
       13 C-NMR (DMSO, 50 MHz): 141.35, 141.21, 140.17, 139.46 (all quaternary carbon atoms); 129.56, 129.09, 128.79, 127.99, 127.28, 126.70, 126.60, 125.55 (all CH). 
     Example 6 
     Radical anions and the corresponding E° are shown in the following Table 1: 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Products 
                 E° (V vs SCE) 
               
               
                   
                   
               
             
             
               
                   
                 Cis-1,2-di-spirobifluorenyl-ethylene (III) 
                 −1.95 
               
               
                   
                 SPIROTRUXENE (VIII) 
                 −2.55 
               
               
                   
                 SBF FUMARYL KETONE (X) 
                 −1.18 
               
               
                   
                 1,3-DICO (XI) 
                 −1.50 
               
               
                   
                 1,4-DICO (XII) 
                 −1.40 
               
               
                   
                 TRICO (XIII) 
                 −1.48 
               
               
                   
                   
               
             
          
         
       
     
     REFERENCES 
     
         
         1. Haas G. and Prelog V., Helv. Chim. Acta (1969) 52, 1202-1218. 
         2. Aviram A et al., J. Am. Chem. Soc. (1988) 110, 5687-92. 
         3. “Molecular Electronics: science and technology” A. Aviram and M. Ratner editors, Annals of the New York Academy of Science Vol. 1852 (1998) 
         4. B. S. Furniss, A. J. Annaford, P. W. G. Smith and A. R. Tatchell in: Vogel&#39;s textbook of practical organic chemistry, 5th ed, Longman, UK 1989. 
         5. Organic Electrochemistry”, 4 a  Ed., Henning Lund e Ole Hamerich Eds., Marcel Dekker Inc, NY, (2001). 
         6. A. J. Bard, L. R. Faulkner, “Electrochemical methods” Wiley, New York. II ed. 2001. 
         7. J. G. Laquindanum, H. E. Katz, A. Dodabalapur and A. J. Lovinger, J. Am. Chem. Soc., (1996) 118, pp 11331-11332. 
         8. Gore P. H., Chem. Rev. (1955), 55, p. 229.