The photophysics and two-photon absorption of a series of quadrupolar and tribranched molecules: The role of the edge substituent

A series of quadrupolar and tribranched molecules were synthesized in order to examine the role of the edge substituents on their photophysical and two-photon absorption properties. Two-photon absorption cross sections, δ, of the molecules were determined in THF solution using a two-photon excited fluorescence technique with femtosecond pulsed excitation. The quadrupolar molecules contained a fluorene or alcoxy-substituted phenylene central core together with various electron accepting edge substituents such as pyridine, terpyridine, phthalimide and naphthalimide. The tribranched molecules contained triphenylamine at the center and terpyridine or phthalimide substituents at the periphery. It was found that edge phthalimide substituent favour high δ values. δ Values as high as 1660 GM and 1500 GM were obtained from the phthalimide-fluorene-phthalimide and phthalimide-phenylene-phthalimide molecules, respectively; in the case of the tribranched molecule with a phthalimide substituent, a δ-value of 1200 GM was found.