Organometallic Complexes for Nonlinear Optics. 42. Syntheses, Linear, and Nonlinear Optical Properties of Ligated Metal-Functionalized Oligo(p-phenyleneethynylene)s

Abstract

A combination of UV-vis-NIR spectroscopy, femtosecond Z-scan measurements, and time-dependent density functional theory (TD-DFT) calculations have been used to comprehensively investigate the linear optical and nonlinear optical (NLO) properties of pi-delocalizable metal-functionalized oligo(phenyleneethynylene)s. A range of unsymmetrically or symmetrically end-functionalized mono-, di-, tri-, penta-, hepta-, and nona(phenyleneethynylene)s were synthesized, with larger examples bearing varying numbers of 2,5-di(hexyloxy)phenyl groups to ensure sufficient solubility of the metal complex derivatives. The effect of incorporating varying numbers of solubilizing substituents in the OPE bridge, peripheral group modification, OPE lengthening, coligand variation, and metal location in the OPE on the linear optical properties has been established, with the first three molecular modifications resulting in significant changes in the optical absorption maxima. TD-DFT calculations reveal that the most intense transition in the linear optical spectra is localized on the OPE bridge and involves excitation from acetylenic to cumulenic molecular orbitals that are not greatly spatially separated from one another. The nonlinear optical properties are dominated by two-photon absorption, which for all but 1,4-{trans-[RuCl(dppm)(2)]C[triple bond]C}(2)C(6)H(4) appears as a band around 11,400 cm(-1) and a sharp increase of nonlinear absorption at frequencies >17,000 cm(-1). Surprisingly, there is relatively little influence of the length of the OPE bridge on the magnitude of the two-photon absorption cross sections, which are in the range 300-1000 GM.

Long‐Range Corrected DFT Calculations of First Hyperpolarizabilities and Excitation Energies of Metal Alkynyl Complexes

“…According to the experimental UV‐Vis data, further extending the conjugation from 5 to 6 leads to a blue‐shift in the lowest energy CT band (Table ). Previous studies, for similar species have suggested that the observed blue‐shift in the absorption maximum is due to the internal rotation of the phenylene groups about the C(ipso)‐C≡ bonds in solution. Studies on related systems have shown that the TD‐DFT calculations on a single conformer fail to explain the absorption band envelopes.…”

Linear Optical, Quadratic and Cubic Nonlinear Optical, Electrochemical, and Theoretical Studies of “Rigid‐Rod” Bis‐Alkynyl Ruthenium Complexes

“…Low‐energy linear optical behavior is expected to be significantly affected by planarity of the π bridge, as shown by previous related studies . We assessed the influence of the orientation of the alkynyl ligands with respect to the metal center, as well as the relative orientation of the planes of the two alkynyl ligands, on the low‐lying linear optical data in 16M , the smallest bis‐alkynyl complex in the set.…”

Twists and turns: Studies of the complexes and properties of bimetallic complexes featuring phenylene ethynylene and related bridging ligands

“…As the alkynyl ligand is extended from arylacetylide derivatives to ethynyl tolan (diphenylacetylene) based ligands, a similar pattern of behaviour emerges [192]. [197,198]. However, the alkynyl ligand is not entirely innocent even in the C 7 H 7 -alkynyl systems, as is evidenced by the observation of hyperfine coupling to substituents on the alkynyl ligand in EPR and ENDOR spectra [207] and slow formation of bis(vinylidene) dimers through C  -C  radical homo-coupling reactions which take place in solutions of the alkynyl [208] and diynyl [209] radicals (Scheme 6).…”