Spiro-linked oligofluorenes and derivatives: Molecular design and theoretical study of one- and two-photon absorption properties

A series of spiro-linked oligofluorenes and derivatives have been theoretically studied with DFT/B3LYP/6-31 G(d) associated with Zindo/SOS method. The increase of two-photon absorption (TPA) cross-sections of spiro-linked oligofluorenes with chain length can be expressed by formula lgδTPA(N) = αlgN + lgδTPA(N = 1). (N is the number of fluorene rings in the molecule). The effects of Si center and interconnection pattern of fluorene rings on TPA response are discussed. The introduction of ethyne and ethene conjugated-bridges can further increase TPA cross-sections in longer wavelength range. The maximum one-photon absorption wavelengths of all molecules are less than 400 nm, which demonstrate spiro-linked oligofluorenes and derivatives exhibit at the same time strong two-photon absorption and good transparency.