Dependence of the Two-Photon Absorption Cross Section on the Conjugation of the Phenylacetylene Linker in Dipolar Donor−Bridge−Acceptor Chromophores

Abstract

The nonlinear optical properties of four isomeric dipolar two-photon chromophores are compared. The chromophores consist of a carbazole electron donor coupled to a naphthalimide electron acceptor by a phenylacetylene bridge. By variation of the connectivity of the bridge at the phenyl groups, four compounds with 0, 1, and 2 meta linkages are synthesized. The linear and nonlinear optical properties of these compounds are measured. Despite similar linear absorption cross sections, the two-photon absorption cross section delta of the all-meta compound is almost a factor of 10 lower than the all-para compound. By taking the detailed molecular conformations into account in order to calculate accurate dipole moment changes, we find that the decrease in delta results largely from the decreased charge transfer ability with increasing number of meta linkages. We find that a two-state model can be used to predict semiquantitatively the observed trend in delta on the basis of the linear optical properties of the molecules. This work illustrates the dramatic effect the ground-state polarizability can have on the nonlinear optical response of organic compounds and also provides a way to quantify the ability of meta linkages to inhibit charge transfer in their ground-state configuration.

Electron transfer dynamics and excited state branching in a charge-transfer platinum(ii) donor–bridge-acceptor assembly

“…In turn, 3 and the "donor-bridge" dyad 4 were prepared from cis-Pt(PBu 3 ) 2 Cl 2 . Thus, [trans-acetylide-Pt-Cl] dyads 3 and 4 were formed in a reaction of cis-Pt(PBu 3 ) 2 Cl 2 with 4-ethynyl-N-octyl-1,8-naphthalimide 59 and N-(4-ethynylbenzyl)-phenothiazine, 60 respectively, in boiling i Pr 2 NH in the absence of CuI. The Ptcontaining starting material cis-Pt(PBu 3 ) 2 Cl 2 was prepared via the reaction of PtCl 2 with a slightly sub-stoichiometric quantity of P n Bu 3 at r.t. to yield the four-coordinate complex in moderate yields (60-70%) with absolute cis stereochemistry.…”

Femtosecond Two-Photon Absorption Spectroscopy of Poly(fluorene) Derivatives Containing Benzoselenadiazole and Benzothiadiazole

“…These effects are associated with the transition dipole moment (μ) and dipole moment change (Δμ), which govern the 2PA cross section in organic materials [21]. However, although increasing the polymeric chain seems like an interesting option to increase the π-conjugation length, which in turn would increase the nonlinearity, after a given point the polymeric structure start to bend, strongly affecting the π-conjugation planarization, causing a great reduction in the 2PA cross section [22]. In this context, push–pull polymers have gained attention because their structure allows for the obtainment of great charge redistribution at the excited state, providing a prodigious nonlinear optical response.…”

Temperature Effect on the Two-Photon Absorption Spectrum of All-trans-β-carotene

“…8 Due to the quadratic dependence with the irradiance as well as the distinct electric-dipole selection rules, the 2PA process has been extensively employed in various kinds of applications, from biology to physics. 9−11 Although in the past few years the 2PA process has been widely investigated in organic compounds because of its great technological appeal, most of these studies were concentrated in intramolecular effects, such as the electronic delocalization, 12 degree of molecular planarity, 13,14 intramolecular charge transfer process, 15 bond length alternation, 16 cooperative enhancement between branches, 17 and so on. However, there are only a few studies concerning the relationship between the 2PA processes and external effects, such as its dependence with the temperature.…”