Theoretical Study Of The Electrical Properties Of Several Functional Organic Molecules

In this work, theoretical studies on several organic molecules used as molecular wire have been performed by using density functional theory(DFT)at the B3LYP/6-311+G^* level. Electronic character of these organic molecules mentioned in this work has been explored detailedly. Moreover, mechanism of the charge transfer in alkyl chain has been discussed. In this paper, we will describe the electronic character as well as their effect on the charge transfer phenomenon in different organic molecules from three chapters respectively.In chapter 3, the effect of molecular chain length and different end group on the charge transfer in alkyl chain have been explored by studing two different series of alkyl chains: C_nH_2n+1OH(n=10,12,14,16,18)å’ŒC₁₂H₂₅X(X=Cl,OH,NH₂). Calculated results showed that the influence of end group on the electronic character(viz. the HOMO-LUMO gap related to the charge transfer character of the organic molecules)of these alkyl chains is very strong. However, the effect of chain length on the electronic character of these alkyl chains is small, which is in agreement with our previous experimental results. Moreover, there is a strong correlation between HOMO-LUMO gaps and the electron potentials of these alkyl chains. Following studies for the spin density distribution (related to the hole location in the charge transfer) on these alkyl chains indicated that hole is located on the molecular orbital which is used for the charge transfer (viz. electron wave function delocalized on the whole linear chains) in alkyl chains. As a result, it can be predict that the charge transfer in alkyl chains should be a hole transfer mechanism, not an electron transfer mechanism.In chapter 4, the effect of the unsaturated bond and their different position on the HOMO-LUMO gap, frontier molecular orbitals and charge transfer character of the organic alkyl chain has been explored by introducing double or triple bond into saturated dodecanol. Calculated results showed that the HOMO energy of dodecanol will be decreased by introducing unsaturated bond. Moreover, the effect of double bond on the HOMO energy is large than that of triple bond because of theÏ€conjugated character of the double bond, which is in correlated with their corresponding stability character. According to our frontier molecular orbital distribution analysis, almost all of the frontier orbitals in unsaturated molecules are located conjugated structure except for the LUMO orbital of the monoene system which is independent on the conjugated character. The charge transfer ability in unsaturated organic linear molecules should be decreased as: triene > alkyne > monoene.In chapter 5, the electronic structures of two bipheylethylene isomers have been studied carefully by using the same theoretical method. Our calculated results indicated that the charge transfer characters in these two isomers are different because of their different electronic character and coplanarity induced by different conformation. Moreover, we found that electronic character of the bipheylethylene will be influenced by introducing hydroxyl though their geometry structure is almost independent on the induced hydroxyl group.