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 cha rge-separated (CS) states of a series of supposedly rigid donor-{bridge}-ac ceptor systems that are being used experimentally to study electron-transfe r 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 ac ceptor chromophores. The extent of structural distortion experienced by a C S system depends on the stiffness of the charged chromophores and the conne cting bridge, and on the relative orientation of the two chromophores.