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-sections, the push-pull dipolar and quadrupolar chromophores have both attracted major attention. In order to provide the basis of molecular engineering and comparison of these two families of molecules, we implement multivalence-bond states models based on measurable parameters. The analytical expressions of the resonant two-photon absorption cross-sections are derived for both families of molecules. Difference and likeness in a number of features are outlined by comparing the results obtained for these molecular systems. The multivalence-bond states models provide useful guidelines for the design of push-pull dipolar and quadrupolar chromophores with enhanced two-photon absorption cross-sections. (C) 2000 American Institute of Physics. [S0021-9606(00)30134-9].