title: Large Hyperpolarizabilities at Telecommunication-Relevant Wavelengths in Donor-Acceptor-Donor Nonlinear Optical Chromophores.
abstract: OctopolarD2-symmetric chromophores, based on the MPZnM supermolecular motif in which (porphinato)zinc(II) (PZn) and ruthenium(II) polypyridyl (M) structural units are connected via ethyne linkages, were synthesized. These structures take advantage of electron-richmeso-arylporphyrin or electron-poormeso-(perfluoroalkyl)porphyrin macrocycles, unsubstituted terpyridyl and 4'-pyrrolidinyl-2,2';6',2″-terpyridyl ligands, and modulation of metal(II) polypyridyl-to-(porphinato)zinc connectivity, to probe how electronic and geometric factors impact the measured hyperpolarizability. Transient absorption spectra obtained at early time delays (tdelay< 400 fs) demonstrate fast excited-state relaxation, and formation of a highly polarized T1excited state; the T1states of these chromophores display expansive, intense T1→ Tnabsorption manifolds that dominate the 800-1200 nm region of the NIR, long (μs) triplet-state lifetimes, and unusually large NIR excited absorptive extinction coefficients [ε(T1→ Tn) ∼ 105M-1cm-1]. Dynamic hyperpolarizability (βλ) values were determined from hyper-Rayleigh light scattering (HRS) measurements, carried out at multiple incident irradiation wavelengths spanning the 800-1500 nm spectral domain. The measured βHRSvalue (4600 ± 1200 × 10-30esu) for one of these complexes, RuPZnRu, is the largest yet reported for any chromophore at a 1500 nm irradiation wavelength, highlighting that appropriate engineering of strong electronic coupling between multiple charge-transfer oscillators provides a critical design strategy to realize octopolar NLO chromophores exhibiting large βHRSvalues at telecom-relevant wavelengths. Generalized Thomas-Kuhn sum (TKS) rules were utilized to compute the effective excited-state-to-excited-state transition dipole moments from experimental linear-absorption spectra; these data were then utilized to compute hyperpolarizabilities as a function of frequency, that include two- and three-state contributions for both βzzzand βxzxtensor components to the RuPZnRu hyperpolarizability spectrum. This analysis predicts that the βzzzand βxzxtensor contributions to the RuPZnRu hyperpolarizability spectrum maximize near 1550 nm, in agreement with experimental data. The TKS analysis suggests that relative to analogous dipolar chromophores, octopolar supermolecules will be likely characterized by more intricate dependences of the measured hyperpolarizability upon irradiation wavelength due to the interactions among multiple different β tensor components.
authors.affiliation: Department of Chemistry, Duke University, French Family Science Center, 124 Science Drive, Durham, North Carolina 27708-0346, United States; Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: Animesh
authors.initials: A
authors.lastname: Nayak
authors.affiliation: Department of Chemistry, Duke University, French Family Science Center, 124 Science Drive, Durham, North Carolina 27708-0346, United States; Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: Jaehong
authors.initials: J
authors.lastname: Park
authors.affiliation: Department of Chemistry, University of Leuven , B-3001 Leuven, Belgium.
authors.forename: Kurt
authors.initials: K
authors.lastname: De Mey
authors.affiliation: Department of Chemistry, Duke University , French Family Science Center, 124 Science Drive, Durham, North Carolina 27708-0346, United States.
authors.forename: Xiangqian
authors.initials: X
authors.lastname: Hu
authors.affiliation: Department of Chemistry, University of Pennsylvania , 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: Timothy V
authors.initials: TV
authors.lastname: Duncan
authors.affiliation: Department of Chemistry, Duke University, French Family Science Center, 124 Science Drive, Durham, North Carolina 27708-0346, United States; Department of Biochemistry, Duke University, Durham, North Carolina 27710, United States; Department of Physics, Duke University, Durham, North Carolina 27708-0346, United States.
authors.forename: David N
authors.initials: DN
authors.lastname: Beratan
authors.affiliation: Department of Chemistry, University of Leuven , B-3001 Leuven, Belgium.
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
authors.affiliation: Department of Chemistry, Duke University , French Family Science Center, 124 Science Drive, Durham, North Carolina 27708-0346, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Therien