Active control of the distribution products a chemical reaction was demonstrated by using method based on principle quantum mechanical interference. Hydrogen iodide (HI) molecules were simultaneously excited above their ionization threshold two competing pathways. These paths absorption three ultraviolet photons frequency ω 1 and one vacuum photon 3 = 3ω . The HI + I signals modulated as phase between lasers varied, with signal lagging 150° ± 15°. A mechanism consisting autoionization...

The conjugated polyelectrolyte PPESO3 features a poly(phenylene ethynylene) backbone substituted with anionic 3-sulfonatopropyloxy groups. is quenched very efficiently (KSV > 106 M-1) by cationic energy transfer quenchers in an amplified quenching process. In the present investigation, steady-state and picosecond time-resolved fluorescence spectroscopy are used to examine of series cyanine dyes via singlet−singlet transfer. goal this work understand mechanism characterize important...

A series of poly(arylene ethynylene) (PAE) conjugated polyelectrolytes (CPEs) have been prepared using palladium-mediated (Sonogashira) coupling chemistry. The consists five pairs polymers that share the same backbone. One member each pair contains anionic sulfonate (R−SO3-) side groups, whereas other cationic bis-alkylammonium (R-N+−R-N+−R) groups. repeat unit structure backbone a bis(alkoxy)phenylene-1,4-ethynylene alternating with second arylene ethynylene moiety, and different arylenes...

Coherence, signifying concurrent electron-vibrational dynamics in complex natural and man-made systems, is currently a subject of intense study. Understanding this phenomenon important when designing carrier transport optoelectronic materials. Here, excited state simulations reveal ubiquitous pattern the evolution photoexcitations for broad range molecular systems. Symmetries wavefunctions define specific form non-adiabatic coupling that drives quantum transitions between states, leading to...

The optical and photophysical properties of phenylacetylene dendritic macromolecules based on unsymmetrical branching are investigated using steady-state time-dependent spectroscopy. Monodendrons, up to the fourth generation, characterized with without a fluorescent perylene trap at core. higher generation monodendrons exhibit high molar extinction coefficients (>10(5) M(-1) cm(-1)) fluorescence quantum yields (65-81%). When is placed core, then typically energy transfer (approximately 90%),...

Adaptive laser pulse shaping has enabled impressive control over photophysical processes in complex molecules. However, the optimal shape that emerges rarely offers straightforward insight into excited-state properties being manipulated. We have shown emission quantum yield of a donor-acceptor macromolecule (a phenylene ethynylene dendrimer tethered to perylene) can be enhanced by 15% through iterative phase modulation excitation pulse. Furthermore, analyzing optimization process and...

The ultrafast dynamics of electronic and vibrational energy transfer between two- three-ring linear poly(phenylene ethynylene) units linked by meta-substitution is studied nonadiabatic molecular simulations. with quantum transitions(1, 2) method used including an "on the fly" calculation potential surfaces couplings. results show that during first 40 fs after a vertical photoexcitation to S2 state, coupling S1 states causes fast populations. A rapid decrease S1−S2 gap observed, reaching...

Non-adiabatic excited-state molecular dynamics is used to study the ultrafast intramolecular energy transfer between two-, three-, and four-ring linear polyphenylene ethynylene chromophore units linked through meta-substitutions. Twenty electronic energies, with their corresponding gradients nonadiabatic coupling vectors were included in simulations. The initial laser excitation creates an exciton delocalized different absorbing two-ring PPE units. Thereafter, we observe directional change...

Solar energy conversion starts with the harvest of light, and its efficacy depends on spatial transfer light to where it can be transduced into other forms energy. Harnessing solar power as a clean source requires continuous development new synthetic materials that photon transport without significant losses. With chemically-controlled branched architectures, dendrimers are ideally suited for these initial steps, since they consist arrays chromophores relative positioning orientations create...

Excited-state nonadiabatic molecular dynamics is used to study energy transfer in dendrimer building blocks, between two-, three-, and four-ring linear polyphenylene ethynylene units linked by meta-substitutions. Upon excitation, dendrimers with these blocks have been shown undergo highly efficient unidirectional transfer. The simulations start initial vertical excitation the S4, localized on two-ring unit. We observe ultrafast directional S4 → S3 S2 S1 electronic transfer, corresponding...

Dendrimers are arrays of coupled chromophores, where the energy each unit depends on its structure and conformation.

By combining step-scan Fourier-transform Michelson interferometry, an infrared microscope, and mercury cadmium telluride focal-plane array image detection we have constructed a mid-infrared spectroscopic imaging system that simultaneously records high-fidelity images spectra of materials from 3500 to 900 cm-1 (2.8 11 µm) at variety spectral resolutions. The fidelity the is determined by pixel number density array. Step-scan principles instrument design details are outlined. Spatial...

Coherent phase control was demonstrated for a bound-to-continuum transition of polyatomic molecule. Three UV photons frequency ω1 and one vacuum ultraviolet (VUV) photon ω3=3ω1 simultaneously excited H2S above its ionization threshold. The parent ion, H2S+, fragment ions, HS+ S+, produced by absorption additional photons, were observed. All three ion signals modulated as the difference between light fields varied.

Femtosecond degenerate pump−probe spectroscopy is used to investigate the ultrafast dynamics of electronic excitations in nanostar dendrimer. The laser wavelength was chosen preferentially excite 2-ring peripheral phenylacetylene chromophores, or 3-ring intermediate chromophores. transients reveal several components with relaxation times ranging from hundred femtoseconds tens picoseconds, depending on excitation wavelength. experimental resulting chromophores are interpreted terms Förster...

The dynamics of fluorescence quenching a conjugated polyelectrolyte by cyanine dye are investigated femtosecond up-conversion and polarization resolved transient absorption. data analyzed with model based on the random walk exciton within polymer chain long-range direct energy transfer between dye. We find that rapid intrachain migration toward complex sites leads to highly efficient transfer, whereas contribution from direct, is negligible. determine actual density complexes along chain. A...

A new series of conjugated polyelectrolytes (CPE) consisting an arylene–ethynylene backbone featuring phenyl (Ph), 2,1,3-benzothiadiazole (BTD), or 4,7-bis(2′-thienyl)-2,1,3-benzothiadiazole (TBT) units have been synthesized and characterized. On each polymer repeat unit the CPEs contain two branched ionic side groups a "triad" carboxylate (R-CO2–Na+) ammonium (R-NH3+Cl–) units, giving polymers six charges per repeat. The photophysical properties were investigated in CH3OH H2O solution by...

The apparently-multicomponent subpicosecond intermolecular dynamics of carbon disulfide liquid are addressed in a unified manner terms an inhomogeneously broadened quantum mechanical harmonic oscillator model for single vibrational coordinate. For (Gaussian) distribution oscillators, the predicts naturally bimodal character liquid, and also spectral evolution effects (spectral narrowing saturation) that observed solutions weakly interacting alkane solvents. unique dynamical signature these...

We present a theoretical investigation of energy transfer in the phenylene ethynelene dendrimer known as nanostar. Data from extensive molecular dynamics simulations are used to model dynamical effects caused by torsional motion phenyl groups. compare rate constants for between two-ring chromophore and three-ring obtained via Förster model, ideal dipole approximation (IDA), transition density cube (TDC) method, which has its limit an exact representation Coulombic coupling. find that with...

We present a sequential molecular dynamics/quantum mechanics (MD/QM) study and steady-state spectroscopy measurements of the nanostar dendrimer (a phenylene−ethynylene attached to ethynylperylene chromophore) determine temperature dependence electronic absorption process. studied as separate units performed MD simulations for each chromophore at 10 300 K effects on structures. The spectrum nanostar, K, was computed using an ensemble 8000 structures chromophore. Quantum mechanical (QM)...

Coherent phase control of the photodissociation CH3I has been achieved by quantum mechanical interference between competing paths. The was accomplished exciting parent molecules with three UV photons frequency ω1 and one VUV photon ω3=3ω1. Varying difference two laser beams resulted in a modulation I+ CH+3 signals, without affecting ion signal. We propose mechanism which occurs over step to produce CH3+I*, followed ionization neutral fragments additional photons.

We have applied the fluorescence upconversion technique to explore electronic excitation energy transfer in unsymmetrical phenylene ethynylene dendrimers. Steady-state emission spectra show that from dendrons core is highly efficient. Ultrafast time-resolved measurements are performed at various wavelengths possibility of assigning absorption band structures exciton localizations. propose a kinetic model describe data. Independent wavelength, typical rise-time value 500 fs measured for...

We report the synthesis, structure and properties of cyanide-bridged dinuclear complex ions [Ru(L)(bpy)(μ-NC)M(CN)5]2−/− (L = tpy, 2,2′;6′,2′′-terpyridine, or tpm, tris(1-pyrazolyl)methane, bpy 2,2′-bipyridine, M Fe(II), Fe(III), Cr(III)) related monomers [Ru(L)(bpy)X]2+ (X CN− NCS−). All monomeric compounds are weak MLCT emitters (λ 650–715 nm, ϕ ≈ 10−4). In Fe(II) Cr(III) systems, cyanide bridge promotes efficient energy transfer between Ru-centered state a Fe(II)- Cr(III)-centered d–d...

Light-harvesting and intramolecular energy funneling are fundamental processes in natural photosynthesis. A comprehensive knowledge of the main structural, dynamic, optical properties that regulate efficiency such can be deciphered through study artificial light-harvesting antennas, capable mimicking systems. Dendrimers some most explored molecules. However, they have to well-defined highly branched conjugated structures, creating gradients guarantee efficient unidirectional transfer....