Large three-photon absorption and intramolecular charge transfer of the bis-donor fluorene-based molecules

Abstract

Three-photon absorption (3PA) of two fluorene-based molecules with D–π–D structural motifs (abbreviated as BPAF and BCZF) has been determined by using a Q-switched Nd: YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 222 and 140×10 −78 cm 6 s 2 for BPAF and BCZF, respectively. AM1 calculations show that attaching different donors changes the charge density distribution of the fluorene skeleton, and it is observed that the 3PA cross-section can be enhanced with increasing intramolecular charge transfer character, measured by the parameter Δ ρ 1/Δ ρ 2/Δ ρ 1′.