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Abstract: We report a theoretical study of intra-molecular electronic coupling in a symmetric DBA (donor–bridge–acceptor) complex, in which a donor electronic site is coupled to an acceptor site by way of intervening orbitals of a molecular bridge unit. In the off-resonant (deep tunneling) regime of electronic transport, the lowest unoccupied molecular orbitals (MO’s) of the DBA system are split into distinguishable donor/acceptor and bridge orbitals. The effect of geometrical changes at the bridge on the donor/acceptor electronic energy manifold is studied for local stretching and bending modes. It is demonstrated that the energy splitting in the manifold of donor/acceptor unoccupied MOs changes in response to such changes, as assumed in simple McConnell-type models. Limitations of the simple models are revealed where the electronic charging of the bridge orbitals correlates with increasing donor/acceptor orbital energy splitting only for stretching but not for bending bridge modes. [Copyright &y& Elsevier]

Abstract: Electron transfer and electronic energy transfer (EET) processes are ways by which different molecules can interact, signalling their state, by EET from a donor (D) to an acceptor (A). This D–A transfer is often observed in an intermolecular process but it can also occur intramolecularly, that is between two bridged parts of a bichromophoric molecule. In this paper we present results pertaining to electronic energy transfer in a newly synthesized rhodamine–azulene (Rh–Az) a bichromophoric molecule, in which a full adder can be implemented. The intramolecular EET rate constant in the Rh–Az molecule was found to be 7.81×109 s−1. [Copyright &y& Elsevier]

Abstract: The experimental strategies and theoretical understanding in transforming molecular conformations with good SHG response functions into polymers with the help of chiral groups are discussed. Chirality plays an important role in designing new types of stable second-order NLO materials. The presence of chiral molecules in the main chain of the polymer introduces acentric conformations and thereby increases the SHG efficiency. On the other hand, for strong donor and acceptor groups between a pi-bridge, large SHG coefficients can be realized at the molecular scale. Chiral molecules are noncentrosymmetric with a nonvanishing electric-dipole-allowed second-order response, which persists in bulk samples also. On the other hand, contributions of magnetic-dipole interactions, which can be strong in chiral materials, allow second-order processes in centrosymmetric materials. Also the polymers incorporated with chiral molecules showed higher response than the standard MNA. This could be due to the chiral component contribution to the electric and magnetic-dipole tensor. [Copyright &y& Elsevier]