We have performed calculations using the TD DFT PBEPBE model with the 6-31G basis set together with COSMO water solvent model (installed on our research group dual processor Opteron servers Linux cluster) of the difference of electron charge density (excited-state - ground-state) for the conjugated cytosine-1,4-bis(N,N-dimethylamino)naphthalene supermolecule and six fatty acid, and two pFA molecules, and visualized the electron charge tunneling associated with certain excited state transitions (see picture).
During the most intense excited state the single electron is hopping (tunneling) from cytosine-1,4-bis(N,N-dimethylamino)naphthalene supermolecule (dark blue cloud of electron hole) to one of pFA molecules (grey cloud of electron). Carbon atoms and their associated covalent bonds are shown as green sticks, hydrogens are in light grey, oxygens – red, nitrogens – blue.
Quantum mechanical electron correlation experiments of the self-assembly of the key components of such artificial minimal living cells show that these cells are complex systems. Only the entire ensemble of PNA, and sensitizer, and pFA, and FA and water molecules is stable and perform quantum photosynthetic processes. Removing the small part of nucleobase, FA and water molecules leads to the structural changes in comparison with realistic structures and differences in comparison with the spectroscopic values of photoexcited electron tunneling from sensitizer (1,4-bis(N,N-dimethylamino)naphthalene to pFA molecules. Removing the main part of nucleobase, and FA and water molecules leads to the degradation of these systems [
8]. The inclusion of ever more water, and fatty acid, and pFA molecules, and waste pieces of the pFA molecules and nucleobase molecules in the structures results in a shift of the absorption spectrum to the red for the artificial protocell photosynthetic centre, leading to an ever closer approach to the real experimental value and indicates the measure of the complexity of this quantum complex system. It is important to say that only QM electron correlation TD-DFT experiments gives results accurately comparable with spectroscopic results and all other more simplified QM methods such as local gradient DFT or
ab initio Hartree-Fock gives structures and spectra far from those experimentally measured.
The correspondence of experimental absorption spectra peaks with our QM calculated ones confirms that our chosen method of designing single electron nano photocells might be useful not only for artificial living organisms but also for wide implementation in the nano photodevices, and molecular computers.
