On the geometry, electrical properties and optical spectra of spirobifluorene type molecules

The calculated geometry of the 2,20,7,70-tetraphenyl-9,90-spirobifluorene, 2,20,7,70-tetrakis(biphenyl-4-yl)-9,90-spirobifluorene and 2,20,7,70-tetrakis(9,90-spirobifluoren-2-yl)- 9,90-spirobifluorene in the electronic ground and lowest singlet excited states was optimised using the semiempirical Austin Model 1 (AM1) method. The electron absorption and luminescence spectra obtained by ZINDO/S method and the electronic polarisabilities and second-order hyperpolarisabilities obtained by the finite-field method in AM1 approach show that the departure from planarity leads to a reduction of the effective conjugation length. This causes the decrease of the above quantities whereas the mutual orientation of torsion angles is much less important. The good agreement between the theoretical (in planar arrangement) and experimental optical data indicate that the spectral properties of the studied molecules originate in the molecular structure and are well interpreted using the semiempirical methods of quantum chemistry. q 2004 Elsevier B.V. All rights reserved.