Molecular engineering of push-pull dipolar and quadrupolar molecules for two-photon absorption: A multivalence-bond states approach

In the search of organic molecules with large two-photon absorption cross-s ections, the push-pull dipolar and quadrupolar chromophores have both attra cted major attention. In order to provide the basis of molecular engineerin g and comparison of these two families of molecules, we implement multivale nce-bond states models based on measurable parameters. The analytical expre ssions of the resonant two-photon absorption cross-sections are derived for both families of molecules. Difference and likeness in a number of feature s are outlined by comparing the results obtained for these molecular system s. The multivalence-bond states models provide useful guidelines for the de sign of push-pull dipolar and quadrupolar chromophores with enhanced two-ph oton absorption cross-sections. (C) 2000 American Institute of Physics. [S0 021-9606(00)30134-9].