Design a donor bridge acceptor system (D-B-A) using quantum mechanics methods
Abstract
The geometry optimization for the structures of molecules under study and other properties have been calculated using density functional method with (B3LYP) and 6-31G(d,p) level and Austen model (AM1) semiempirical method. The aim of this work is to calculate the electronic properties for aminotulene molecule as an electron donor molecule, as well as study the electronic properties for bromotulene molecule as an electron acceptor and aminosalicylic molecule as a bridge between donor and acceptor, then grouping these molecules together in one entity to form donor bridge acceptor system (D-B-A). The results show that the total energy rises from donor to bridge to acceptor. As regarding to the HOMO energy for donor molecule, the latter was more than that of acceptor molecule and both these HOMO energies are more than that of bridge molecule, but when designing the donor bridge acceptor molecule, the HOMO energy was the least. This result was similar when calculating LUMO energy but the only difference being the LUMO energy for (D-B-A) was a little higher than that of bridge. With respect to electron affinity (Eea), then both donor and acceptor molecules have electron affinity more than that for bridge, but for (D-B-A) molecule the electron affinity was the least, while ionization potential (IP) value increased from donor to bridge to acceptor then decreased again when (D-B-A) was built. The electronegativity property for bridge, acceptor and (D-B-A) is close together, whereas for the donor it was the least. Finally, it have been estimated the vibration spectrum for all donor, bridge and acceptor using DFT-(B3LYP) and for (D-B-A) it is estimated using Austin model (AM1) which they have been illustrated in this paper. These properties make this system a good (D-B-A) for transporting electrons from donor to acceptor throughout the bridge, thus when a photon collides donor molecule, then it will release an electron because donor molecule has lowest ionization potential of about 7.3 eV, on the other hand bridge has more electronegativity than that of donor, and thus it has high tendency to attract this released electron, which in turn will transmit this electron to acceptor molecule.
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