Large predicted changes in geometry accompanying charge separation in various "rigid" multichromophoric systems in the gas phase: An ab initio MO study

UHF/3-21G theory has been used to calculate the gas phase structures of charge-separated (CS) states of a series of supposedly rigid donor-{bridge}-acceptor systems that are being used experimentally to study electron-transfer processes. It is found that, for most of the systems studied, substantial changes in the interchromophore separation, ranging from 5 to 17 Angstrom, accompany the charge separation process, and that these changes are driven by strong Coulombic interactions between the charged terminal donor and acceptor chromophores. The extent of structural distortion experienced by a CS system depends on the stiffness of the charged chromophores and the connecting bridge, and on the relative orientation of the two chromophores.