A comparative study of electronic structure, one-photon absorption and two-photon absorption properties of octupolar oligofluorenes and their dipolar counterparts is presented by using AM1 and ZINDO-SOS methods. The conjugation length and molecular dimension importantly affect TPA cross-section values. The maximum TPA cross-section increases in proportion to N-alpha (alpha = 2.41 and 2.24), where N is the number of fluorene moieties in dipolar molecules and each arm of octupolar analogs. (C) 2004 Elsevier B.V. All rights reserved.