Nonlinear Optical Properties of D-π-A-π-D Type Oligomers with Different Conjugation Length

Abstract

The conjugation length-dependent nonlinear optical properties of fluorenone-based linear conjugated oligomers have been investigated by experimental and theoretical methods. Infrared spectra and the steady-state absorption spectra show that the increase of conjugated unit could enhance the stretching vibration peaks of C=C and lead to a red-shift of the absorption peaks. Meanwhile, the two-photon fluorescence (TPF) intensity is gradually enhanced with the increase of excitation energy, and the TPF efficiency is obviously higher after the introduction of fluorene-ethylene units. The sum-overstates approach was used to model the two-photon absorption (TPA) cross-sections of oligomers, and the theoretical values agree well with the experimental data obtained from the femtosecond open-aperture z-scan technique. The results exhibit that the extension of conjugated system indeed plays a role in the improvement of TPA behavior of oligomers.

Solvent dependent linear and nonlinear optical properties of triphenylamine unit incorporated difluoroboron β-diketonate complexes

“…Organic ICT compounds are ideal candidates as third-order nonlinear optical materials because of their inherent high hyperpolarizabilities [35][36][37]. Among these molecules, the quadrupolar D-π-A-π-D structure is highlighted for its excellent nonlinear optical properties [38][39][40][41], with large twophoton absorption (TPA) cross-sections [42,43]. The intramolecular charge transfer, which occurs in systems containing both donor and acceptor parts, will influence the TPA properties strongly [44,45].…”

“…The intramolecular charge transfer, which occurs in systems containing both donor and acceptor parts, will influence the TPA properties strongly [44,45]. Different strategies like modifications of donor or acceptor moieties and the adjustment of the conjugation length have been attempted to increase the TPA cross sections [43,[46][47][48][49]. The ICT and the charge distributions also have a significant effect on the nonlinear optical properties of the molecules [50].…”