Theoretical Study Of Chromophores For Biological Sensing: Understanding The Mechanism Of Rhodol Based Multi-Chromophoric Systems

Development of two-photon fluorescent probes can aid in visualizing the cellular environment. Multi-chromophore systems display complex manifolds of electronic transitions, enabling their use for optical sensing applications. Time-Dependent Density Functional Theory (TDDFT) methods allow for accurate predictions of the optical properties. These properties are related to the electronic transitions in the molecules, which include two-photon absorption cross-sections. Here we use TDDFT to understand the mechanism of aza-crown based fluorescent probes for metals sensing applications. Our findings suggest changes in local excitation in the rhodol chromophore between unbound form and when bound to the metal analyte. These changes are caused by a charge transfer from the aza-crown group and pyrazol units toward the rhodol unit. Understanding this mechanism leads to an optimized design with higher two-photon excited fluorescence to be used in medical applications

Cations Modulate Actin Bundle Mechanics, Assembly Dynamics, And Structure

Actin bundles are key factors in the mechanical support and dynamic reorganization of the cytoskeleton. High concentrations of multivalent counterions promote bundle formation through electrostatic attraction between actin filaments that are negatively charged polyelectrolytes. In this study, we evaluate how physiologically relevant divalent cations affect the mechanical, dynamic, and structural properties of actin bundles. Using a combination of total internal reflection fluorescence microscopy, transmission electron microscopy, and dynamic light scattering, we demonstrate that divalent cations modulate bundle stiffness, length distribution, and lateral growth. Molecular dynamics simulations of an all-atom model of the actin bundle reveal specific actin residues coordinate cation-binding sites that promote the bundle formation. Our work suggests that specific cation interactions may play a fundamental role in the assembly, structure, and mechanical properties of actin bundles

New Two-Photon Absorbing Bodipy-Based Fluorescent Probe: Linear Photophysics, Stimulated Emission, And Ultrafast Spectroscopy

The synthesis and comprehensive linear spectroscopic and nonlinear optical properties of a new BODIPY-based fluorene-containing derivative 4,4-difluoro-8-(4-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}phenyl)-1,3,5,7-tetramethyl-2,6-di[(9,9-di{2-[2-(2-methoxyethoxy)ethoxy]ethyl}-9H-fluoren-2-yl)ethynyl]-4-bora-3a,4a-diaza-s-indacene (1) are reported. The steady-state absorption, emission, and excitation anisotropy spectra along with fluorescence lifetimes of 1 were analyzed in organic solvents of different polarity. The degenerate two-photon absorption (2PA) spectrum of 1 was obtained over a broad spectral range by the open aperture Z-scan method using 1 kHz femtosecond excitation, and the 2PA cross section had a maximum value of ∼400 GM. The one-photon stimulated emission depletion spectrum of 1 was determined by a fluorescence quenching method with values of stimulated emission cross sections close to the corresponding ones of the ground state linear absorption. The nature of ultrafast relaxation processes in 1 was analyzed by a transient absorption femtosecond pump-probe technique, and the characteristic times of intramolecular relaxations between the excited electronic states (\u3c150 fs) and solvation dynamics (4-6 ps) were determined. Efficient superluminescence emission of 1 was observed in solution under one- and two-photon femtosecond pumping. Detailed analysis of the singlet excitations in 1 was performed by a time-dependent density functional theory (TD-DFT) method. Three one-photon and two two-photon absorbing states were predicted in the wavelength range investigated. A reactive handle was included in the meso-position of the BODIPY chromophore to facilitate future bioconjugation or functionalization for bioimaging applications

Polymeric Luminescent Zn(Ii) And Cd(Ii) Dicarboxylates Decorated By Oxime Ligands: Tuning The Dimensionality And Adsorption Capacity

Ten Zn(II) and Cd(II) metal-organic materials were synthesized and studied by the X-ray method. Among these 10 structures, two represent binuclear clusters, and two are one-dimensional (1D) coordination polymers, while five are laminar two-dimensional (2D) solids and one is the three-dimensional (3D) framework. The investigation has been aimed at rational design of coordination polymers decorated by oxime ligands to increase the accessible adsorption area in these newly synthesized solids. The ligands used include three aliphatic dicarboxylic acids, HOOC-(CH2)n-COOH [n = 1, 2, 4 corresponding to malonic (H2mal), succinic (H2suc), and adipic (H2adi) acids], and three neutral oxime ligands [pyridine-2-aldoxime (2-pyao), pyridine-4-aldoxime (4-pyao), and 1,2-cyclohexanedionedioxime (Niox)]. These novel hybrid solids with the compositions [Zn2(suc)2(2-pyao)4] ·2H2O 1, [Cd2(suc)(2-pyao)4(H 2O)2][BF4]2 2, [Cd(suc)(2-pyao) 2]n 3, [Zn(mal)(4-pyao)(H2O)]n 4, [Cd(mal)(4-pyao)(H2O)]n 5, [Zn(suc)(4-pyao)]n 6, [Zn(adi)(4-pyao)2]n 7, {[Cd(adi)(4-pyao) 2]·dmf}n 8, [Zn(adi)(Niox)]n 9, and [Cd(adi)(Niox)]n 10 [dmf - N,N\u272-dimethylformamide] demonstrate a variable class of coordination supramolecular architectures dictated by the distinctions in the metals\u27 and oxime ligands\u27 coordination capacities and preferences, and length and flexibility of the dicarboxylic linkers. The discrete aggregates 1 and 2 differ by the components\u27 ratio and conformation of the bridging succinate anion; compounds 3 and 7 are 1D arrays, and compounds 4, 5, 6, 8, and 9 represent 2D layers of different topologies. Compound 10 is a 3D grid afforded by the concerted contribution of the longest in this series adipate anion, and the bigger atomic radius Cd(II) vs. Zn(II). The adsorptive properties of 7 and 9 are reported. For the laminar solid 9, the quantum chemical simulations of the adsorption capacity are in line with the experimental results. All new materials reveal dual green-blue wavelength emission in the solid state. © 2014 American Chemical Society

Mechanism Of Nonlinear Optical Enhancement And Supramolecular Isomerism In 1D Polymeric Zn(Ii) And Cd(Ii) Sulfates With Pyridine-4-Aldoxime Ligands

Interaction of zinc(II) and cadmium(II) sulfates with pyridine-4-aldoxime (4-pyao) and pyridine-4-amidoxime (4-pyamo) ligands resulted in four 1D metal-organic materials (MOMs) with identical composition, [M(SO 4)A2(H2O)2]n, where M = Zn(II), A = 4-pyao for 1, M = Cd(II), A = 4-pyao for 2, M = Zn(II), A = 4-pyamo for 3, M = Cd(II), A = 4-pyamo for 4, and mononuclear [Zn(SO4)(4- pyamo)2(H2O)3] 5. New coordination polymers represent the mixed-ligand supramolecular isomers different by the twisting of two pyridine-4-oxime ligands in the metal coordination environments, and crystallizing in the different space groups. Conformational preferences and nonlinear optical properties of the 4-pyao and 4-pyamo complexes were investigated using density functional theory. Spectral properties of 1-3 have been also evaluated. The solid-state emission of 1D polymers 1-3 appears to be ligand-based, as the positions of the emission maxima remain practically unchanged from free ligand to complexes. The enhancement of luminescence and two-photon absorption in polymers in comparison with the pure ligands is attributed to the chelation of the ligand to the metal center. The detailed mechanism of this enhancement upon complex formation is analyzed and can be used in future design of metal-organic nonlinear optical materials. © 2014 American Chemical Society

Molecular Packing In Organic Solar Cell Materials: Insights From The Emission Line Shapes Of P3Ht/Pcbm Polymer Blend Nanoparticles

Semiconducting polymer devices have seen tremendous progress in development of material and device designs, while device efficiencies have made substantial gains. Still, the effect of material morphology on the optoelectronic properties of semiconducting polymers is not completely understood even though these materials make up the active device layer. In this study we use computational methods to simulate different poly(3-hexylthiophene) (P3HT) morphologies, predict their emission spectra, and compare them to experimentally observed emission spectra for P3HT nanoparticles. We use published X-ray diffraction data on P3HT polymorphs to build the molecular models of nanodomains that differ in the side-chain packing. The atomic and electronic structures of both nanodomains are studied with the force field, Hartree-Fock, CIS, and density functional theory methods. The results confirm the coexistence of type I and II nanodomains, where the shift of the backbones in the same stack is determined by the differences in side-chain packing. Upon excitation, the polymer chains in type II domain are free to slide to their optimal arrangement in the stack, whereas in type I domain this sliding is hindered by the steric repulsion of the side chains and the chains are essentially constrained to keep the ground state geometry. These nanodomains, therefore, differ in their emission spectra: type I emission has a single 0-0 vibronic band, while type II demonstrates pronounced vibronic progression. In agreement with Frenkel exciton theory, splitting of the excited state depends on the longitudinal shift of the π-systems. However, we find that due to the constraints arising from P3HT being confined in nanosized particles, the type I nanodomain increasingly appears as an additional emitter that exhibits J-aggregate character. As a result, a pronounced vibronic structure appears as PCBM blending ratios increase, as opposed to the changes in emission profile due to a different degree of disorder present in weakly coupled H-aggregates. These findings are distinct from those made for bulk P3HT materials. © 2014 American Chemical Society

Mechanism of Nonlinear Optical Enhancement and Supramolecular Isomerism in 1D Polymeric Zn(II) and Cd(II) Sulfates with Pyridine-4-aldoxime Ligands

Interaction of zinc­(II) and cadmium­(II) sulfates with pyridine-4-aldoxime (4-pyao) and pyridine-4-amidoxime (4-pyamo) ligands resulted in four 1D metal–organic materials (MOMs) with identical composition, [M­(SO₄)­A₂(H₂O)₂]_<i>n</i>, where M = Zn­(II), A = 4-pyao for <b>1</b>, M = Cd­(II), A = 4-pyao for <b>2</b>, M = Zn­(II), A = 4-pyamo for <b>3</b>, M = Cd­(II), A = 4-pyamo for <b>4</b>, and mononuclear [Zn­(SO₄)­(4-pyamo)₂(H₂O)₃] <b>5</b>. New coordination polymers represent the mixed-ligand supramolecular isomers different by the twisting of two pyridine-4-oxime ligands in the metal coordination environments, and crystallizing in the different space groups. Conformational preferences and nonlinear optical properties of the 4-pyao and 4-pyamo complexes were investigated using density functional theory. Spectral properties of <b>1</b>–<b>3</b> have been also evaluated. The solid-state emission of 1D polymers <b>1</b>–<b>3</b> appears to be ligand-based, as the positions of the emission maxima remain practically unchanged from free ligand to complexes. The enhancement of luminescence and two-photon absorption in polymers in comparison with the pure ligands is attributed to the chelation of the ligand to the metal center. The detailed mechanism of this enhancement upon complex formation is analyzed and can be used in future design of metal–organic nonlinear optical materials

Mechanism of Nonlinear Optical Enhancement and Supramolecular Isomerism in 1D Polymeric Zn(II) and Cd(II) Sulfates with Pyridine-4-aldoxime Ligands

Interaction of zinc­(II) and cadmium­(II) sulfates with pyridine-4-aldoxime (4-pyao) and pyridine-4-amidoxime (4-pyamo) ligands resulted in four 1D metal–organic materials (MOMs) with identical composition, [M­(SO₄)­A₂(H₂O)₂]_<i>n</i>, where M = Zn­(II), A = 4-pyao for <b>1</b>, M = Cd­(II), A = 4-pyao for <b>2</b>, M = Zn­(II), A = 4-pyamo for <b>3</b>, M = Cd­(II), A = 4-pyamo for <b>4</b>, and mononuclear [Zn­(SO₄)­(4-pyamo)₂(H₂O)₃] <b>5</b>. New coordination polymers represent the mixed-ligand supramolecular isomers different by the twisting of two pyridine-4-oxime ligands in the metal coordination environments, and crystallizing in the different space groups. Conformational preferences and nonlinear optical properties of the 4-pyao and 4-pyamo complexes were investigated using density functional theory. Spectral properties of <b>1</b>–<b>3</b> have been also evaluated. The solid-state emission of 1D polymers <b>1</b>–<b>3</b> appears to be ligand-based, as the positions of the emission maxima remain practically unchanged from free ligand to complexes. The enhancement of luminescence and two-photon absorption in polymers in comparison with the pure ligands is attributed to the chelation of the ligand to the metal center. The detailed mechanism of this enhancement upon complex formation is analyzed and can be used in future design of metal–organic nonlinear optical materials

Mechanism of Nonlinear Optical Enhancement and Supramolecular Isomerism in 1D Polymeric Zn(II) and Cd(II) Sulfates with Pyridine-4-aldoxime Ligands

Interaction of zinc­(II) and cadmium­(II) sulfates with pyridine-4-aldoxime (4-pyao) and pyridine-4-amidoxime (4-pyamo) ligands resulted in four 1D metal–organic materials (MOMs) with identical composition, [M­(SO₄)­A₂(H₂O)₂]_<i>n</i>, where M = Zn­(II), A = 4-pyao for <b>1</b>, M = Cd­(II), A = 4-pyao for <b>2</b>, M = Zn­(II), A = 4-pyamo for <b>3</b>, M = Cd­(II), A = 4-pyamo for <b>4</b>, and mononuclear [Zn­(SO₄)­(4-pyamo)₂(H₂O)₃] <b>5</b>. New coordination polymers represent the mixed-ligand supramolecular isomers different by the twisting of two pyridine-4-oxime ligands in the metal coordination environments, and crystallizing in the different space groups. Conformational preferences and nonlinear optical properties of the 4-pyao and 4-pyamo complexes were investigated using density functional theory. Spectral properties of <b>1</b>–<b>3</b> have been also evaluated. The solid-state emission of 1D polymers <b>1</b>–<b>3</b> appears to be ligand-based, as the positions of the emission maxima remain practically unchanged from free ligand to complexes. The enhancement of luminescence and two-photon absorption in polymers in comparison with the pure ligands is attributed to the chelation of the ligand to the metal center. The detailed mechanism of this enhancement upon complex formation is analyzed and can be used in future design of metal–organic nonlinear optical materials