Electrochemical oligomerization of arenemethylidenes. Attempts to synthesize low bandgap systems
| Autor: | Michael Hanack, Ursula Röhrig, Klaus-Michael Mangold, Cäcilia Maichle-Mössmer |
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| Rok vydání: | 1993 |
| Předmět: |
Mechanical Engineering
Metals and Alloys Cationic polymerization Condensed Matter Physics Electrochemistry Oligomer Electronic Optical and Magnetic Materials Dielectric spectroscopy law.invention Coulometry chemistry.chemical_compound Monomer chemistry Mechanics of Materials law Polymer chemistry Materials Chemistry Thiophene Electron paramagnetic resonance |
| Zdroj: | Synthetic Metals. 60:199-210 |
| ISSN: | 0379-6779 |
| DOI: | 10.1016/0379-6779(93)91280-f |
| Popis: | The electrochemical oligomerization of the arenemethylidenes, 1,3-dihydro-bis-1,3-(2-thienylmethylidene)-isothianaphthene (1b), 1,3-dihydro-bis-1,3-[2-(N-methylpyrryl)methylidene]isothianaphthene (4b), 1,3-dihydro-bis-1,3-(2-thienylmethylidene)thieno[3,4-c]thiophene (5b), 2,5-dihydro-bis-2,5-(2-thienylmethylidene)thiophene (6b), 1,3-dihydro-bis-1,3-(2-thienylmethylidene)isothianaphthene-2-oxide (1a), 1,3-dihydro-bis-1,3-[2-(N-methylpyrryl)methylidene]isothianaphthene-2-oxide (4a), 1,3-dihydro-bis-1,3-(2-thienylmethylidene)thieno[3,4-c]thiophene-1-oxide (5a) and 2,5-dihydro-bis-2,5-(2-thienylmethylidene)thiophene-1-oxide (6a), is investigated by cyclovoltammetry, coulometry, spectroelectrochemistry (UV-Vis-NIR, EPR) and a.c. impedance spectroscopy. Detailed spectroelectrochemical investigation of the oxidation process of compounds 1a, 1b, 4a, 4b, 5a, 5b, 6a and 6b reveals red-shifted absorptions after oxidation indicating the formation of larger π-electron systems. The oxidatively formed layers are electroactive as shown by independent cyclovoltammetry and spectroelectrochemistry measurements; the layers show a reversible switching behaviour between the oxidized and reduced forms. The reactive side of the arenemethylidene precursors in electrochemical oligomerization is determined by blocking possible linking positions with methyl groups. The 4,4′-disubstituted 1,3-dihydro-bis-1,3-(4-methyl-2-thienylmethylidene)isothianaphthene (2b) is oxidatively oligomerizable. The 5,5′-disubstituted 1,3-dihydro-bis-1,3-(5-methyl-2-thienylmethylidene)isothianaphthene (3b) does not form oligomer layers on the electrode due to the methyl-blocked 5,5′-(α,α′) positions and 3b exhibits hyperfine structure in the EPR spectrum. From this it is concluded that the monomer units within an oligomer chain of polyarenemethylidenes are α-α linked. The bandgap values of the polyarenemethylidenes are determined from UV-Vis-NIR spectra to be in the range 1.8–2.1 eV. The conductivity of the oxidized oligomer layers is higher than the reduced layers as shown by a.c. impedance spectroscopy. 2,5-Bis-(di-2-thienylmethylidene)-2,5-dihydrothiophene (7) is not oxidatively oligomerizable due to the formation of stable triheteroaryl methyl cationic structures. |
| Databáze: | OpenAIRE |
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