Peculiarity Of Ethylenedioxy Group In Formation Of Conductive Charge-Transfer Complexes Of Bis(Ethylenedioxy) -Dibenzotetrathiafulvalene (BEDC-DBTTF)

Abstract

Abstract The electronic and molecular structures and charge transfer (CT) complex formation of a new electron donor molecule; bis(ethy1enedioxy)-dibenzotetrathiafulvalene (BEDO-DBTTF), were studied from the point of the peculiar ability of ethylenedioxy group in delivering conductive solid complexes. The BEDO-DBTTF molecules afforded 37 solid complexes with 40 kinds of electron acceptor molecules belonging to 5 systems; TCNQ, quinone, fluorene, percyano and nitrophenyl systems. The infrared and ultraviolet-visible-near infrared spectra of the complexes were examined to study the ionicity of their ground states in solid. A plot of CT transition energies and the difference of redox potentials; Δ E(DA), of donor and acceptor molecules indicated that 10 complexes have neutral ground state. No definitely identified back CT bands were observed in the 4 complexes of completely ionic ground state. 23 complexy of partially ionic ground state gave CT transitions below 5×103 cm−1 and are highly conductive. The presence of the ethylenedioxy group in REDO-DBTTF provided wide variety of conductive complexes regardless the size and shape of acceptor molecules, with smaller degree of CT (γ≥0.3), from combination with much weaker acceptor molecules (Δ E(DA)≤ 0.53) than expected for conventional TTF·TCNQ system (γ≥0.5, Δ E(DA)≤0.34) and with donor molecule excess in content. These features are very much resemblance to those of BEDO-TTF which affords a number of metallic complexes and are ascribed to peculiar ability of ethylenedioxy group to assemble self-aggregated donor assemblies. In spite of such similarity, the partially ionic complexes of BEDO-DBTTF are not metallic, maybe due to the lack of the side-by-side intermolecular sulfur**sulfur short contacts that is predicted based on the molecular geometry consideration. Single crystal growth of BEDO-DBTTF complexes was not much successful. 2,5-Dimethyl- and 2,5-dimethoxy-TCNQ complexes, which reside near the boundary of the partial CT and neutral states, afforded complexes with different ionicities, conductivities and optical properties. The crystal structures of neutral complexes of 2,5-dimethyl- and 2,5-dimethoxy-TCNQ as well as that of neutral donor molecules were determined.