139 research outputs found
Diquat Derivatives: Highly Active, Two-Dimensional Nonlinear Optical Chromophores with Potential Redox Switchability
In this article, we present a detailed study of structureâactivity relationships in diquaternized 2,2âČ-bipyridyl (diquat) derivatives. Sixteen new chromophores have been synthesized, with variations in the amino electron donor substituents, Ï-conjugated bridge, and alkyl diquaternizing unit. Our aim is to combine very large, two-dimensional (2D) quadratic nonlinear optical (NLO) responses with reversible redox chemistry. The chromophores have been characterized as their PF_6^â salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Their visible absorption spectra are dominated by intense Ï â Ï^* intramolecular charge-transfer (ICT) bands, and all show two reversible diquat-based reductions. First hyperpolarizabilities ÎČ have been measured by using hyper-Rayleigh scattering with an 800 nm laser, and Stark spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities ÎČ_0. The directly and indirectly derived ÎČ values are large and increase with the extent of Ï-conjugation and electron donor strength. Extending the quaternizing alkyl linkage always increases the ICT energy and decreases the E_(1/2) values for diquat reduction, but a compensating increase in the ICT intensity prevents significant decreases in Stark-based ÎČ_0 responses. Nine single-crystal X-ray structures have also been obtained. Time-dependent density functional theory clarifies the molecular electronic/optical properties, and finite field calculations agree with polarized HRS data in that the NLO responses of the disubstituted species are dominated by âoff-diagonalâ ÎČ_(zyy) components. The most significant findings of these studies are: (i) ÎČ_0 values as much as 6 times that of the chromophore in the technologically important material (E)-4âČ-(dimethylamino)-N-methyl-4-stilbazolium tosylate; (ii) reversible electrochemistry that offers potential for redox-switching of optical properties over multiple states; (iii) strongly 2D NLO responses that may be exploited for novel practical applications; (iv) a new polar material, suitable for bulk NLO behavior
Evolution of Linear Absorption and Nonlinear Optical Properties in V-Shaped Ruthenium(II)-Based Chromophores
In this article, we describe a series of complexes with electron-rich cis-{Ru^(II)(NH_3)_4}^(2+) centers coordinated to two pyridyl ligands bearing N-methyl/arylpyridinium electron-acceptor groups. These V-shaped dipolar species are new, extended members of a class of chromophores first reported by us (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845â4859). They have been isolated as their PF_6â salts and characterized by using various techniques including ^1H NMR and electronic absorption spectroscopies and cyclic voltammetry. Reversible Ru^(III/II) waves show that the new complexes are potentially redox-switchable chromophores. Single crystal X-ray structures have been obtained for four complex salts; three of these crystallize noncentrosymmetrically, but with the individual molecular dipoles aligned largely antiparallel. Very large molecular first hyperpolarizabilities ÎČ have been determined by using hyper-Rayleigh scattering (HRS) with an 800 nm laser and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d â Ï^* metal-to-ligand charge-transfer (MLCT) and Ï â Ï^* intraligand charge-transfer (ILCT) bands. The latter measurements afford total nonresonant ÎČ_0 responses as high as ca. 600 Ă 10^(â30) esu. These pseudo-C_(2v) chromophores show two substantial components of the ÎČ tensor, ÎČ_(zzz) and ÎČ_(zyy), although the relative significance of these varies with the physical method applied. According to HRS, ÎČ_(zzz) dominates in all cases, whereas the Stark analyses indicate that ÎČ_(zyy) is dominant in the shorter chromophores, but ÎČ_(zzz) and ÎČ_(zyy) are similar for the extended species. In contrast, finite field calculations predict that ÎČ_(zyy) is always the major component. Time-dependent density functional theory calculations predict increasing ILCT character for the nominally MLCT transitions and accompanying blue-shifts of the visible absorptions, as the ligand Ï-systems are extended. Such unusual behavior has also been observed with related 1D complexes (Coe, B. J. et al. J. Am. Chem. Soc. 2004, 126, 3880â3891)
Synthesis, Structures, and Optical Properties of Ruthenium(II) Complexes of the Tris(1-pyrazolyl)methane Ligand
Four new complex salts [Ru^(II)Cl(Tpm)(L^A)_2][PF_6]_n [Tpm = tris(1-pyrazolyl)methane; n = 1, L^A = pyridine (py) 1 or ethyl isonicotinate (EIN) 2; n = 3, L^A = N-methyl-4,4âČ-bipyridinium (MeQ^+) 3 or N-phenyl-4,4âČ-bipyridinium (PhQ^+) 4] have been prepared and characterized. Electronic absorption spectra show intense d â Ï^* metal-to-ligand charge-transfer (MLCT) absorption bands, while cyclic voltammetry reveals a reversible Ru^(III/II) wave, accompanied by quasireversible or irreversible L^A-based reductions for all except 1. Single crystal X-ray structures have been obtained for 1âąMe_2CO, 2, and 3âąMe_2CO. For 2â4, molecular first hyperpolarizabilities ÎČ have been measured in acetonitrile solutions via the hyper-Rayleigh scattering (HRS) technique at 800 nm. Stark (electroabsorption) spectroscopic studies on the MLCT bands in frozen butyronitrile allow the indirect estimation of static first hyperpolarizabilities ÎČ_0. The various physical data obtained for 3 and 4 are compared with those reported previously for related cis-{Ru^(II)(NH_3)_4}^(2+) species [Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845]. TD-DFT calculations on the complexes in 1â4 confirm that their lowest energy absorption bands are primarily Ru^(II) â L^A MLCT in character, while Ru^(II) â Tpm MLCT transitions are predicted at higher energies. DFT agrees with the Stark, but not the HRS measurements, in showing that ÎČ_0 increases with the electron-accepting strength of L^A. The 2D nature of the chromophores is evidenced by dominant ÎČ_(xxy) tensor components
A prenylation inhibitor (sodium phenylacetate) differently affects MCF-7 cell death when ras is overexpressed, partly involving p42/44, JNK and p38 kinase activations
1 - ArticleBackground: Sodium phenylacetate (NaPa) inhibits breast cancer cell proliferation decreasing prenylation of small G proteins including Ras. Materials and Methods: Aponecrosis induced by NaPa in MCF-7 and MCF-7ras breast cancer cells was evaluated by measuring Annexin V/PI labelling by flow cytometry. Specific inhibitors of p42/44 (PD 98059), p38 (SB 600125) and JNK (SP 202190) in association with NaPa were also tested. Mitogen-activated kinase (MAPK) activation was measured by immunoprecipitation. Results: NaPa induced cell death more efficiently (80%) in the MCF-7ras cells compared to the MCF-7 cells (60%). NaPa activated ERK 112 and its combination with PD 98059 decreased cell death in the MCF-7ras cells in contrast to the MCF-7 cells. Combination of NaPa with specific inhibitors of both JNK and p38 kinases also partly decreased MCF-7ras cell death. Conclusion: NaPa induced cell death differently when ras was overexpressed in breast cancer cells, partly involving p42/44, JNK and p38 pathways
Line-narrowing spectroscopy in amorphous solids through polarization detection of spectral holes. I. Principles
Detection of spectral satellite holes by polarization spectroscopy is proposed as a method to measure the line-narrowed electronic absorption spectrum of a large mol. in an amorphous solid at low temp. The linewidths of the zero-phonon holes yield information about mol. dephasing and the correlation of the inhomogeneous distribution of the 2 mol. transitions involved in the hole-burning and the detection step. Constructive or destructive interference of the signal light field with an intentionally admixed background light field yields information on the symmetry of vibronic states
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