Determination of the rotational isomerization rate along carbon-carbon single bonds in solution.

The temperature- and viscosity-dependent rotational isomerization time constant () along the C-C˙ bond of CFBrCF radical in solution was measured using femtosecond infrared spectroscopy after photodissociating the I atom from CFBrCFI. Three density functional theory (DFT) functionals, ωB97XD, APFD, and B3LYP were used with the aug-cc-pVTZ basis set to calculate the required parameters in calculating using Kramers' theory of reaction rates. The measured was consistent with the value calculated using the vibrational frequencies and rotational barriers of the related compounds calculated by DFT method with ωB97XD/aug-cc-pVTZ.

Photoexcitation Dynamics of V-PYRRO/NO Investigated Using Femtosecond Time-Resolved Infrared Spectroscopy.

Diazeniumdiolates spontaneously release nitric oxide (NO) in aqueous solutions. Therefore, protected diazeniumdiolates have been developed for the controlled administration of NO to specific targets. Diazeniumdiolates with photoprotecting groups are useful for spatiotemporal NO delivery.

Photoexcitation Dynamics of 4-Aminopthalimide in Solution Investigated Using Femtosecond Time-Resolved Infrared Spectroscopy.

Excited-state intramolecular proton transfer (ESIPT) reactions are crucial in photoresponsive materials and fluorescent markers. The fluorescent compound 4-aminophthalimide (4-AP) has been reported to exhibit solvent-assisted ESIPT in protic solvents, such as methanol, wherein the solvent interacts with 4-AP to form a six-membered hydrogen-bonded ring that is strengthened upon excitation. Although the controversial observation of ESIPT in 4-AP has been extensively studied, the molecular mechanism has yet to be fully explored.

Effect of Electron-donating Group on NO Photolysis of {RuNO} Ruthenium Nitrosyl Complexes with N O Lgands Bearing π-Extended Rings.

In this study, we introduced the electron-donating group (-OH) to the aromatic rings of Ru(salophen)(NO)Cl (0) (salophenH =N,N'-(1,2-phenylene)bis(salicylideneimine)) to investigate the influence of the substitution on NO photolysis and NO-releasing dynamics. Three derivative complexes, Ru((o-OH) -salophen)(NO)Cl (1), Ru((m-OH) -salophen)(NO)Cl (2), and Ru((p-OH) -salophen)(NO)Cl (3) were developed and their NO photolysis was monitored by using UV/Vis, EPR, NMR, and IR spectroscopies under white room light. Spectroscopic results indicated that the complexes were diamagnetic Ru(II)-NO species which were converted to low-spin Ru(III) species (d , S=1/2) and released NO radicals by photons.

Investigating the Photodissociation Dynamics of CFBrCFI in CCl through Femtosecond Time-Resolved Infrared Spectroscopy.

The photodissociation dynamics of CFBrCFI in CCl at 280 ± 2 K were investigated by probing the C-F stretching mode from 300 fs to 10 μs after excitation at 267 nm using time-resolved infrared spectroscopy. The excitation led to the dissociation of I or Br atoms within 300 fs, producing the CFBrCF or CFICF radicals, respectively. All nascent CFICF underwent further dissociation of I, producing CFCF with a time constant of 56 ± 5 ns.

Dynamics of Irreversible NO Release from Photoexcited Molsidomine.

Molsidomine (SIN-10), an orally administered NO-delivery drug for vasodilation, cannot be used to alleviate hypertensive crisis because it releases NO at a slow rate. SIN-10 may be used to treat sudden cardiac abnormalities if the rapid and immediate release of NO is achieved via photoactivation. The photodissociation dynamics associated with the NO release process from SIN-10 in CHCl was investigated using time-resolved infrared spectroscopy.

Rotational Isomerization of Carbon-Carbon Single Bonds in Ethyl Radical Derivatives in a Room-Temperature Solution.

The rotational isomerization of 1,2-disubstituted ethyl radical derivatives, reaction intermediates often found in the reaction of 1,2-disubstituted ethane derivatives, has never been measured because of their short lifetime and ultrafast rotation. However, the rotational time constant is critical for understanding the detailed reaction mechanism involving these radicals, which determine the stereoisomers of compounds produced via the intermediates. Using time-resolved infrared spectroscopy, we found that the CFBrCF radical in a CCl solution rotationally isomerizes with a time constant of 47 ± 5 ps at 280 ± 2 K.

Visible-light NO photolysis of ruthenium nitrosyl complexes with NO ligands bearing π-extended rings and their photorelease dynamics.

NO photorelease and its dynamics for two {RuNO} complexes, Ru(salophen)(NO)Cl (1) and Ru(naphophen)(NO)Cl (2), with salen-type ligands bearing π-extended systems (salophenH = ,'-(1,2-phenylene)-bis(salicylideneimine) and naphophenH = ,'-1,2-phenylene-bis(2-hydroxy-1-naphthylmethyleneimine)) were investigated. NO photolysis was performed under white room light and monitored by UV/Vis, EPR, and NMR spectroscopies. NO photolysis was also performed under 459 and 489 nm irradiation for 1 and 2, respectively.

Photoacid-induced aqueous acid-base reactions probed by femtosecond infrared spectroscopy.

Acid-base reactions involving an excited photoacid have typically been investigated at high base concentrations, but the mechanisms at low base concentrations require clarification. Herein, the dynamics of acid-base reactions induced by an excited photoacid, pyranine (DA), were investigated in the presence of azide ion (N) in DO solution using femtosecond infrared spectroscopy. Specifically, the spectral characteristics of four species (DA, electronically excited DA (DA*), the conjugate base of DA* (A*), and the conjugate base of DA (A)) were probed in the spectral region of 1400-1670 cm in the time range of 1 ps-1 μs.

Photoexcitation dynamics of bromodiphenyl ethers in acetonitrile-d studied by femtosecond time-resolved infrared spectroscopy.

The efficient decomposition of polybrominated diphenyl ethers (PBDEs), onetime prevalent flame retardants, is central to the reduction of their harmful effects on human health. PBDE photodecomposition is a promising method, but its mechanism and products are not well understood. The photoexcitation dynamics of 3- and 4-bromodiphenyl ethers (BDE-2 and BDE-3) in CDCN were studied from 0.

Midwavelength Infrared Colloidal Nanowire Laser.

Realizing bright colloidal infrared emitters in the midwavelength infrared (or mid-IR), which can be used for low-power IR light-emitting diodes (LEDs), sensors, and deep-tissue imaging, has been a challenge for the last few decades. Here, we present colloidal tellurium nanowires with strong emission intensity at room temperature and even lasing at 3.6 μm (ω) under cryotemperature.

Modulations of a Metal-Ligand Interaction and Photophysical Behaviors by Hückel-Möbius Aromatic Switching.

In organometallic complexes containing π-conjugated macrocyclic chelate ligands, conformational change significantly affects metal-ligand electronic interactions, hence tuning properties of the complexes. In this regard, we investigated the metal-ligand interactions in hexaphyrin mono-Pd(II) complexes and , which exhibit a redox-induced switching of Hückel-Möbius aromaticity and subsequent molecular conformation, and their effect on the electronic structure and photophysical behaviors. In Möbius aromatic , the weak metal-ligand interaction leads to the π electronic structure of the hexaphyrin ligand remaining almost intact, which undergoes efficient intersystem crossing (ISC) assisted by the heavy-atom effect of the Pd metal.

Photodissociation Dynamics of Nitric Oxide from -Acetylcysteine- or -Acetylpenicillamine-bound Roussin's Red Ester.

The photochemical release of nitric oxide (NO) from a NO precursor is advantageous in terms of spatial, temporal, and dosage control of NO delivery to target sites. To realize full control of the quantitative NO administration from photoactivated NO precursors, it is necessary to have detailed dynamical information on the photodissociation of NO from NO precursors. We synthesized two new water-soluble Roussin's red esters (RREs), [Fe(μ--acetylcysteine)(NO)] and [Fe(μ--acetylpenicillamine)(NO)], which have five times longer lifetime than the well-known [Fe(μ-cysteine)(NO)].

Dynamics of photodissociation of nitric oxide from -nitrosylated cysteine and -acetylated cysteine derivatives in water.

Cysteine and N-acetylated cysteine derivatives are ubiquitous in biological systems; they have thiol groups that bind NO to form S-nitrosothiols (RSNOs) such as S-nitrosocysteine (CySNO), S-nitroso-N-acetylcysteine (NacSNO), and S-nitroso-N-acetylpenicillamine (NapSNO). Although they have been utilised as thermally or catalytically decomposing NO donors, their photochemical applications are yet to be fully explored owing to the lack of photodissociation dynamics. To this end, the photoexcitation dynamics of these RSNOs in water at 330 nm were investigated using femtosecond time-resolved infrared (TRIR) spectroscopy over a broad time range encompassing the entire reaction, which includes the primary reaction, secondary reactions of the reaction intermediates, and product formation.

-Oxoisocorroles: Tunable Antiaromaticity by Metalation and Coordination of Lewis Acids as Well as Aromaticity Reversal in the Triplet Excited State.

The corrole derivative -oxoisocorrole has been theoretically predicted to be antiaromatic, despite its formally cross conjugated electronic system. In this study, this prediction has been experimentally proven by the facile preparation of -oxoisocorrole via the oxidation of a free corrole with MnO and its comprehensive characterization using NMR, UV/vis absorption, FT-IR, and transient-absorption spectroscopy, cyclic voltammetry, and X-ray diffraction analysis. Furthermore, the free base -oxoisocorrole was metalated by treatment with Ni(acac), PdCl(PhCN), and Zn(OAc) to give the corresponding metal complexes.

Conformer-Specific Photodissociation Dynamics of CFICFI in Solution Probed by Time-Resolved Infrared Spectroscopy.

The photodissociation dynamics of CFICFI in solution was investigated from 0.3 ps to 100 μs, after the excitation of CFICFI with a femtosecond UV pulse. Upon excitation, one I atom is eliminated within 0.

Photorelease Dynamics of Nitric Oxide from Cysteine-Bound Roussin's Red Ester.

Nitric oxide (NO) can either boost or impede the growth of cancer cells depending on its concentration. Therefore, any anticancer treatment using NO requires precisely controlled NO administration to the target cells in terms of dosage and timing. In this context, photochemically activated NO donors were actively explored, but their detailed NO-releasing dynamics, which is crucial for their use, is not known yet.

Excited-State Aromaticity of Gold(III) Hexaphyrins and Metalation Effect Investigated by Time-Resolved Electronic and Vibrational Spectroscopy.

Expanded porphyrins with appropriate metalation provide an excellent opportunity to study excited-state aromaticity. The coordinated metal allows the excited-state aromaticity in the triplet state to be detected through the heavy-atom effect, but other metalation effects on the excited-state aromaticity were ambiguous. Herein, the excited-state aromaticity of gold(III) hexaphyrins through the relaxation dynamics was revealed via electronic and vibrational spectroscopy.

Two-electron transfer stabilized by excited-state aromatization.

The scientific significance of excited-state aromaticity concerns with the elucidation of processes and properties in the excited states. Here, we focus on TMTQ, an oligomer composed of a central 1,6-methano[10]annulene and 5-dicyanomethyl-thiophene peripheries (acceptor-donor-acceptor system), and investigate a two-electron transfer process dominantly stabilized by an aromatization in the low-energy lying excited state. Our spectroscopic measurements quantitatively observe the shift of two π-electrons between donor and acceptors.

Complete photodissociation dynamics of CFI in solution.

Photodissociation dynamics of CF2I2 in cyclohexane were evaluated by probing the C-F stretching mode over a wide time range after ultraviolet excitation using femtosecond infrared spectroscopy. After the ultrafast (<0.2 ps) state-selective photodissociation of CF2I2 as in the gas phase (267 nm excitation led to exclusive three-body dissociation (CF2 + I + I), 350 nm to exclusive two-body dissociation (CF2I + I), and 310 nm to a mixture of three- and two-body dissociations), various secondary reactions were observed.

Computational Probing of Watson-Crick/Hoogsteen Breathing in a DNA Duplex Containing N1-Methylated Adenine.

DNA breathing is a local conformational fluctuation spontaneously occurring in double-stranded DNAs. In particular, the possibility of individual base pairs (bps) in duplex DNA to flip between alternate bp modes, i.e.

Photodissociation of CFICFI in solid para-hydrogen: infrared spectra of anti- and gauche-˙CFI radicals.

The photolysis of 1,2-diiodotetrafluoroethane (CF2ICF2I) has served as a prototypical system in ultrafast reaction dynamics. Even though the intermediates, anti- and gauche-iodotetrafluoroethyl (˙C2F4I) radicals, have been characterized with electron diffraction and X-ray diffraction, their infrared spectra are unreported. We report the formation and infrared identification of these radical intermediates upon ultraviolet photodissociation of CF2ICF2I in solid para-hydrogen (p-H2) at 3.

Insilico direct folding of thrombin-binding aptamer G-quadruplex at all-atom level.

The reversible folding of the thrombin-binding DNA aptamer G-quadruplexes (GQs) (TBA-15) starting from fully unfolded states was demonstrated using a prolonged time scale (10-12 μs) parallel tempering metadynamics (PTMetaD) simulation method in conjunction with a modified version of the AMBER bsc1 force field. For unbiased descriptions of the folding free energy landscape of TBA-15, this force field was minimally modified. From this direct folding simulation using the modified bsc1 force field, reasonably converged free energy landscapes were obtained in K+-rich aqueous solution (150 mM), providing detailed atomistic pictures of GQ folding mechanisms for TBA-15.

Symmetry-breaking charge transfer in the excited state of directly linked push-pull porphyrin arrays.

Herein, we revealed a symmetry-breaking charge transfer (SBCT) process in the excited state of a directly linked push-pull porphyrin dyad (AD) and triad (ADA) via spectroscopic measurements including steady-state absorption and fluorescence, time-resolved fluorescence (TRF), femtosecond transient absorption (fs-TA), and time-resolved infrared (TRIR) measurements. Unprecedented broad fluorescence spectra were observed for porphyrin arrays in polar solvents; these were attributed to the existence of a charge transfer state as evidenced by the TRF measurements. TA measurements also revealed emerging features of a CT state for AD and ADA in polar solvents.