The quantum chemical simulations of two, three, four and six anisotropic random-walk stilbene and azo-dyes based molecular devices in ground state were performed by using ab initio Hartree-Fock (HF), Møller-Plesset (MP2) and Density Functional Theory (DFT) B3PW91 model methods in 6-311G** basis set.
Two variable anisotropic random-walk stilbene based molecular device is designed from carbazole (Cz), 1,4-phenilenediamine (PhDA), stilbene and TCNQ molecules joined with -C2H2- fragment bridges. The geometry optimization of bistilbene molecule was done by HF\6-311G**, stilbene molecule was optimized by DFT B3PW91\6-311G** and that was the basis for the design of stilbene based random walk molecular devices. The planes of phenyles are approximately 43 degrees twisted in ground state.
The two variable random-walk molecular device should be possible to excite by two different wavelengths that corresponds approximately wavelengths of Cz and PhDA investigated by CNDO\S-CI and ZINDO-CI computation methods. After excitation this supermolecule should be deformed by two different ways and after electron tunnelling to acceptor fragment TCNQ this molecule should dissipate the energy moving on the surface by two different ways.
Another kind of two variable random-walk device is designed based on one electron donor fragment and two electron acceptor fragments: Cz-C6H6-CH=CH-C6H6-TCNQ, NO2. Three variable anisotropic random-walk stilbene based molecular devices are designed by such: Cz, PhDA, N,N,N',N'-tetramethyl-1,4-phenylene-diamine (TeMePhDA), stilbene and TCNQ molecules joined with -C2H2- fragment bridges or by another manner: Cz-C6H6-CH=CH-C6H6-TCNQ, TCNB, NO2. Four variable anisotropic random-walk stilbene based molecular device is designed from Cz, PhDA, stilbene, TCNQ and TCNB molecules joined with -C2H2- fragment bridges. Six variable anisotropic random-walk stilbene based molecular deviceare designed as: Cz, PhDA, TeMePhDA, stilbene TCNQ and TCNB molecules joined with -C2H2- fragment bridges or: Cz, PhDA-C6H6-CH=CH-C6H6-TCNQ, TCNB, NO2.
We have calculated DR1 azo dye molecule: NH2-C6H6-N=N-C6H6-NO2 (P. Lefin et al, Pure Appl. Opt., 1998, vol. 7, p.71). Geometry optimization was done using DFT B3PW91\6-311 model in ground state. The angles <CNN of optimized molecule are approximately 114 and 115 degrees. In this molecule exist weak bondings between bridge nitrogen atoms and phenyle ring closest hydrogen atoms - something like intramolecule hydrogen bondings. These intramolecular hydrogen bondings keep molecule in almost one plane: only 0.015 and 0.005 degrees are between planes and -N=N- bridge. Exist also relatively large charge transfer from donor -NH2 part to acceptor -NO2 part: up to 0.12 electron charge in the ground state. That means that this derivative possesses the charge transfer band in excited state.
Based on DR1 azo dye calculation results were designed two variable random-walk molecular devices: Cz, PhDA-C6H6-N=N-C6H6-NO2 and Cz-C6H6-N=N-C6H6-TCNQ, NO2, three variable random-walk devices: Cz, PhDA, TeMePhDA-C6H6-N=N-C6H6-NO2 and Cz-C6H6-N=N-C6H6-TCNQ, TCNB, NO2, four variable random-walk device: Cz, PhDA-C6H6-N=N-C6H6-TCNQ, NO2 and six variable random-walk devices: Cz, PhDA, TeMePhDA-C6H6-N=N-C6H6-TCNQ, NO2 and Cz, PhDA-C6H6-N=N-C6H6-TCNQ, TCNB, NO2.
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