A new class of push–pull molecules for molecular electronics

In this work, we have found that large conjugated pyridinium betaines, molecules composed by a donor (D) and acceptor (A) pair connected through a long conjugated chain, exhibit an inversion in the expected direction of the electron transfer resulting from photoexcitation. Once the connecting bridge is increased beyond a given size, the electron transfer is predicted to occur in a reversed manner, i.e. from the acceptor to the donor side of the molecule. This effect seems to be associated to an inversion of the spatial localization of the frontier molecular orbitals. We present results for the spatial localization of the frontier molecular orbitals and the theoretical absorption spectra of members of increasing size of a specific family of pyridinium betaines.