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Short laser pulse technology has significantly contributed to biomedical research, especially via nonlinear optical microscopy. Coherent anti-Stokes Raman scattering (CARS) microscopy is a label-free, chemical-selective method that is growing in importance as improved methods and light sources develop. Here we discuss different approaches to laser source development for CARS microscopy and highlight the advantages of a multimodal CARS microscope, illustrated by selected applications in biomedical research. [c] 2010 Optical Society of America OCIS codes: 170.5810, 180.4315, 300.6230.

Random orientation of molecules within a sample Leads to blurred observations of chemical reactions studied from the Laboratory perspective. Methods developed for the dynamic imaging of molecular structures and processes struggle with this, as measurements are optimally made in the molecular frame. We used laser alignment to transiently fix carbon disulfide molecules in space long enough to elucidate, in the molecular reference frame, details of ultrafast electronic-vibrational dynamics during a photochemical reaction. These three-dimensional photoelectron imaging results, combined with ongoing efforts in molecular alignment and orientation, presage a wide range of insights obtainable from time-resolved studies in the molecular frame.

The femtosecond pump-probe spectroscopic study results for the electronic structure and dynamics of isolated adenine, thymine dimers and the adenine-thymine base pair are presented. The observation from the photoelectron spectra indicate short-lived [pi][pi]* and n[pi]* perturbed populations in the hydrogen-bound dimers as compared to the monomers.

The UV chromophores in DNA are the nucleic bases themselves, and it is their photophysics and photochemistry that govern the intrinsic photostability of DNA. Because stability is related to the conversion of dangerous electronic to less-dangerous vibrational energy, we study ultrafast electronic relaxation processes in the DNA base adenine. We excite adenine, isolated in a molecular beam, to its [pi][pi] * state and follow its relaxation dynamics using femtosecond time-resolved photoelectron spectroscopy. To discern which processes are important on which timescales, we compare adenine with 9-methyl adenine. Methylation blocks the site of the much-discussed [pi][sigma]* state that had been thought, until now, minor. Time-resolved photoelectron spectroscopy reveals that, although adenine and 9-methyl adenine show almost identical timescales for the processes involved, the decay pathways are quite different. Importantly, we confirm that in adenine at 267-nm excitation, the [pi][sigma]* state plays a major role. We discuss these results in the context of recent experimental and theoretical studies on adenine, proposing a model that accounts for all known results, and consider the relationship between these studies and electron-induced damage in DNA. dynamics | photochemistry

Optically writable, thermally erasable surface relief gratings in thin Disperse Red 1 polymethyl methacrylate azopolymer films were used to demonstrate an arbitrarily reconfigurable fiber Bragg filter. Gratings were optically written on azopolymer-coated side-polished fiber blocks, and a write-erase-write cycle was demonstrated. Finite difference time domain simulations reveal that this optically reconfigurable device concept can be optimized in a silicon-on-insulator waveguide platform. OCIS codes: 160.5470, 230.1480.

Femtosecond time-resolved photoelectron spectroscopy, which is applied to the dynamics of gas-phase neutral and anionic molecules and clusters, is reviewed. The time-resolved photoelectron spectroscopy can be used for studying the intermolecular and intramolecular dynamics and other fundamental photochemical and photophysical processes.

Numerical studies of femtosecond time-resolved probes of coupled wave packet dynamics in model polyatomic systems are presented. A final-state resolved measure of wave packet dynamics, a low frequency band-pass filter of the signal, which is sensitive to intermode energy flow, is introduced to recover a classical-like picture of energy flow between coupled vibrational modes.

High-repetition-rate (80-MHz) femtosecond infrared pulses are generated by difference frequency mixing (DFM) a femtosecond Ti:sapphire laser with a phase-locked synchronized cw mode-locked Nd:YAG picosecond laser. This DFM scheme is of particular interest for generating ultrashort near-IR pulses ([approximately]10 fs) because group velocity mismatch with a pump pulse can be ignored. The simplicity and the broad wavelength tunability (from the near IR to the mid-IR) of this scheme is demonstrated. Short (125-fs FWHM) optical pulses in the near IR around 1.5 [[micro]meter] are obtained with noncritical type-I phase-matched Li[B.sub.3][O.sub.5]. We also used a similar scheme to generate mid-infrared pulses at 3.0 [[micro]meter] with type-II phase-matched KTiOP[O.sub.4].

Chemical reactions involve the concerted motions of both atoms and electrons as bonds rearrange on the way from reactant to product. Elementary models use a single, one-dimensional (1D) reaction coordinate [...]

Recent research has produced time-resolved photoelectron spectroscopy measurements that distinguish vibrational dynamics from the coupled electronic population dynamics, linked with the photo-induced internal conversion, in a linear unsaturated hydrocarbon chain. This method was demonstrated by studying ultrafast internal conversion in a linear polyene, all-trans 2,4,6,8 decatetraene. It is suggested that this method could offer new views about the scope and timescale for the onset of statistical behaviour in an isolated, energized molecule.

The photoelectron spectroscopic results from studies conducted to determine the effects of methyl substitution on the electronic dynamics of the [alpha],[beta]-enones is presented. The findings indicated that the conical intersection promoting relaxation to the [S.sub.1](n[pi]*) state lifetime differences are attributed to the specific dynamical factors that affect the efficiency of passage through the [S.sub.1][S.sub.0] conical intersection.

The detailed analysis of the excited-state dynamics of isolated adenine in a molecular beam observed by femtosecond time-resolved photoelectron spectroscopy (TRPES) is described. Color-coded map of photoelectron intensity as a function of time delay and kinetic energy is presented.

The femtosecond time-resolved photoelectron spectroscopy is a useful technique for investigating state dynamics in isolated polyatomic molecules. The advantages of the molecular ionization continuum as the final state in polyatomic wavepacket experiments are discussed and the use of electronic structure of the continuum to disentangle electronic from vibrational dynamics is shown.

The applicability of femtosecond time-resolved photoelectron spectroscopy is applied to the study of substituent effects in molecular electronic relaxation dynamics using a series of monosubstituted benzenes as model compounds. Femtosecond excitation to the second PiPi state leads upon time-delayed ionization, to two distinct photoelectron bands having different decay constants.

In the ancient Indian tale of six blind men encountering an elephant, each man approaches the creature from a different direction. One finds the trunk, another a leg, the third [...]

A stereocontrolled total synthesis of (-)-ephedradine A was accomplished by a Rh-catalyzed C-H insertion reaction and a sharpless asymmetric aminohydroxylation reaction. The synthesis features construction of all the secondary amines using the Ns-strategy, including macrocyclination and formation of the two amine bonds by the intramolecular ester-amine exchange reaction and the aza-Wittig reaction.

Alkane reductive elimination provided the first example of a zirconium sandwich compound that underwent haptotropic rearrangement to yield a zwitterionic zirconium sandwich with an n(super 6) indenyl ligand. Reconstitution of n(super 5) hapticity could be achieved by addition of strong donor ligands or by oxidative addition.

Lappert and co-workers prepared the divalent germanium and tin compounds [Me3Si]2Ge and [(Me3Si)2N]2 Sn, which are the classic examples of stable germylenes and stannylenes. It is found that [(Me2Si)N]2Si: is stable at low temperatures in solution and undergoes rapid decomposition above ~0 degree Celsius.

Several groups have measured fluorescence decay times of the DNA/RNA nucleosides and nucleotides in solution. The excited-state lifetimes of the nucleic acid molecules fall in the subpicosecond time scale, suggesting the presence of an ultrafast internal conversion channel for both nucleosides and nucleotides.

The third strand in the triplex inhibits the formation of the TMPyP assembly. Therefore, TMPyP stacking occurs in the major groove of both the d(A)12.d(T)12 and the d(G)12;d(C)12 duplexes.

An aggregation phenomenon of DNA-functionalized gold nanoparticles induced by hybridization of target DNA that does not cross-link the nanoparticles is reported. A colloidal solution of gold nanoparticles with diameters of 5 - 20 nm exhibits a red color, as such nanoparticles have an optical absorption peak around 520 nm caused by surface plasmon resonance.

The synthesis and structure of novel phenylazomethine dendrimers with an aryl amine as the core is reported. The novel dendrimer is applicable as a hole-transport material in an EL device, using metal-assembling properties in which the metal acts as a mediator of the hole transfer.

Two bright, near degenerate pt pt* states for AZ with distinct electronic character and decay dynamics are identified. It is reported that the dissimilar lifetimes of these states suggest different relaxation pathways.

Several researches are conducted on the catalytic formation and transformation of C-N bonds by group 4 complexes. It was reported that imido complex [{(Me2N)C-N(super i)Pr2}2Ti =N(2,6-Me2C6H3)] is a catalyst for alkyne hydroamination and it is determined that the imido group of [{(Me2N)C-(N(super i)Pr)2}2Ti=N(2,6-Me2C6H3) can undergo a clean exchange.