Nanosecond Time-resolved Infrared Spectroscopy Research Articles

Capturing the Long-Lived Photogenerated Electrons in Au/TiO2 upon UV or Visible Irradiation by Time-Resolved Infrared Spectroscopy

Gold nanoparticle modifications for TiO2 (Au/TiO2) can extend the absorption wavelength from UV to visible (Vis) and enhance the photocatalytic performance, thus fueling increasing attention as an emerging photocatalysis strategy. To explore the plasmon-enhanced photocatalytic mechanism and directly unveil the intrinsic properties of Au/TiO2, the decay kinetics of photoelectrons upon UV (355 nm) or Vis (532 nm) excitation are monitored by means of nanosecond time-resolved infrared spectroscopy, which is a unique tool offering observations without interference of the holes. Under UV irradiation, the longer lifetime of photoelectrons observed in Au/TiO2 compared to that in bare TiO2 provides unambiguous evidence for the enhanced charge separation by AuNPs. Under Vis irradiation, the long-lived (hundreds of microseconds) electrons produced by injection from AuNPs into TiO2 upon plasmon excitation are here detected for the first time. Moreover, the effects of TiO2 phase composition and the amount of AuNPs loa...

Photophysics of Singlet and Triplet Intraligand Excited States in [ReCl(CO)3(1-(2-pyridyl)-imidazo[1,5-α]pyridine)] Complexes

Excited-state characters and dynamics of [ReCl(CO)3(3-R-1-(2-pyridyl)-imidazo[1,5-α]pyridine)] complexes (abbreviated ReGV-R, R = CH3, Ph, PhBu(t), PhCF3, PhNO2, PhNMe2) were investigated by pico- and nanosecond time-resolved infrared spectroscopy (TRIR) and excited-state DFT and TD-DFT calculations. Near UV excitation populates the lowest singlet state S1 that undergoes picosecond intersystem crossing (ISC) to the lowest triplet T1. Both states are initially formed hot and relax with ∼20 ps lifetime. TRIR together with quantum chemical calculations reveal that S1 is predominantly a ππ* state localized at the 1-(2-pyridyl)-imidazo[1,5-α]pyridine (= impy) ligand core, with impy → PhNO2 and PhNMe2 → impy intraligand charge-transfer contributions in the case of ReGV-PhNO2 and ReGV-PhNMe2, respectively. T1 is predominantly ππ*(impy) in all cases. It follows that excited singlet and corresponding triplet states have to some extent different characters and structures even if originating nominally from the same preponderant one-electron excitations. ISC occurs with a solvent-independent (CH2Cl2, MeCN) 20-30 ps lifetime, except for ReGV-PhNMe2 (10 ps in CH2Cl2, 100 ps in MeCN). ISC is 200-300 times slower than in analogous complexes with low-lying MLCT states. This difference is interpreted in terms of spin-orbit interaction and characters of orbitals involved in one-electron excitations that give rise to S1 and T1 states. ReGV-R present a unique case of octahedral heavy-metal complexes where the S1 lifetime is long enough to allow for separate spectroscopic characterization of singlet and triplet excited states. This study provides an insight into dynamics and intersystem crossing pathways of low-lying singlet and triplet excited states localized at bidentate ligands bound directly to a heavy metal atom. Rather long (1)IL lifetimes indicate the possibility of photonic applications of singlet excited states.

Femtosecond to Microsecond Photochemistry of a [FeFe]hydrogenase Enzyme Model Compound

The photochemistry and dynamics of a model compound of the active site of the [FeFe]hydrogenase enzyme system have been studied on a wide range of time scales using a unique combination of femtosecond time-resolved infrared spectroscopy, nanosecond time-resolved infrared spectroscopy, and steady-state UV-FTIR methods. Using three different solvents, heptane, acetonitrile, and cyanoheptane, we have observed the rapid formation of solvent adduct species from the first solvation shell of the solute following photolysis of a carbonyl ligand and global fitting techniques have been employed to provide new insights into the ultrafast dynamics of this process. In addition, the use of solvent mixtures has enabled the observation of competitive ligand substitution processes at the newly created coordination site on time scales of a few nanoseconds, shedding new light on the chemical behavior of these enzyme models.

Triplet quantum chain process in the photoisomerization of 9- cis retinal as revealed by nanosecond time-resolved infrared spectroscopy

The mechanism of the photoisomerization of 9- cis retinal has been studied by nanosecond time-resolved infrared spectroscopy. A cyclohexane solution of 9- cis retinal was photoexcited at 349 nm and the subsequent photodynamics were traced. A singular value decomposition (SVD) analysis of the time-resolved infrared data shows that there are two distinct isomerization pathways. One is the triplet pathway that takes place in the picosecond time regime from 9- cis to all- trans. The other involves the energy transfer between the all- trans triplet state and the 9- cis ground state with the resultant 9- cis triplet state subsequently reproducing the all- trans by fast isomerization on the triplet potential surface . This quantum chain process occurs in the microsecond time regime.

Experimental and Theoretical Investigation into the Formation and Reactivity of M(Cp)(CO)2(CO2) (M = Mn or Re) in Liquid and Supercritical CO2 and the Effect of Different CO2 Coordination Modes on Reaction Rates with CO, H2, and N2

Nanosecond time-resolved infrared spectroscopy (TRIR) has been used to study the coordination of CO₂ to the metal centers by UV photolysis of M(Cp)(CO)₃ (M = Mn or Re) in liquid or supercritical CO₂ (scCO₂) solution, which led to the formation of the CO₂ complexes M(Cp)(CO)₂(CO₂). Differences between the positions of the ν(C−O) IR bands of the CO ligands in Mn(Cp)(CO)₂(CO₂) and Re(Cp)(CO)₂(CO₂) suggest that the CO₂ ligand has different coordination modes to the metal centers in these complexes. The kinetic data and the IR spectra of the CO₂, Xe, and heptane complexes provided evidence that the CO₂ coordination mode is η¹-O end-on bound in Mn(Cp)(CO)₂(CO₂), and η²-C,O side-on bound in Re(Cp)(CO)₂(CO₂). These different coordination modes lead to dramatic differences in reactivity with CO, H₂, and N₂, with the Re complexes being significantly less reactive. To provide more evidence for the nature of the CO₂ binding modes, a series of DFT calculations were performed at the B3LYP/SDD-6-311G** level. The calculations supported the experimentally proposed CO₂ coordination modes. A significant charge transfer from Re to CO₂ occurs, resulting in partial oxidation of Re.

The Photoinduced Hydrogen Atom Transfer and trans–cis Isomerization of the C=C Double Bond in 1-(1-Hydroxy-2-naphthyl)-3-(1-naphthyl)-2-propen-1-one and Related Compounds Studied Using Nanosecond Time-Resolved Infrared Spectroscopy

Abstract The mechanism and intermediates of photoinduced hydrogen atom transfer and photoisomerization in 1-(1-hydroxy-2-naphthyl)-3-(1-naphthyl)-2-propen-1-one (1) and 1-(1-methoxy-2-naphthyl)-3-(1-naphthyl)-2-propen-1-one (2) have been investigated using nanosecond time-resolved infrared spectroscopy. For compound 1, a bleach signal was observed at 1575 cm−1 just after the laser excitation and recovered within 2 ms. The transient absorption at 1500 cm−1 decayed with two components of 1 μs and 2 ms, which are due to the triplet state and the ground state tautomer, respectively. On the basis of these results, the potential energy surface of hydrogen atom transfer in compound 1 was deciphered. Upon laser excitation of compound 2, the transient absorption signals at 1528 cm−1 and 1392 cm−1 assigned to the triplet state were observed in addition to the bleach signals at 1664 cm−1 and 1600 cm−1. The bleach signal at 1600 cm−1 remained as a permanent bleaching after the fast recovery with the 1.2 μs time constant. This result indicates that compound 2 underwent trans-to-cis isomerization upon laser excitation. By utilizing the data obtained in stationary and transient IR spectroscopy, we have directly determined the quantum yield of trans-to-cis isomerization to be 0.23 ± 0.01 from the difference in the IR signals.

Time-resolved IR detection and study of an iminooxirane intermediate.

[reaction: see text] Iminooxirane 4 has been generated by the reaction of phenylchlorocarbene (2) with phenyl isocyanate (3) and studied by nanosecond time-resolved infrared spectroscopy. Iminooxirane 4 (1830 cm(-1)) isomerizes to alpha-lactam 5 (1880 cm(-1)) at an observed rate of 3 x 10(4) s(-1). Peak assignments were confirmed by a combination of B3LYP calculations and isotopic labeling. An acyclic transition state was found computationally for the isomerization reaction.

Time-resolved infrared spectra and structures of the excited singlet and triplet states of fluorenone

Nanosecond time-resolved infrared spectroscopy has been used to study the excited electronic states of fluorenone in polar and nonpolar solvents. By using the singular-value-decomposition analysis of the observed time-resolved spectra, infrared spectra of fluorenone in the lowest excited singlet (S 1) and the lowest excited triplet (T 1) states have been obtained for a polar solvent, as well as that in the T 1 state in a nonpolar solvent. The assignments of the CO stretching modes for the S 0, S 1 and T 1 states have been made on the basis of isotopic frequency shifts. The CO stretch frequency of fluorenone in the S 1 state in a polar solvent and those in the T 1 states in polar and nonpolar solvents are much lower than that of the ground state, but are still located in the double-bond frequency region. These findings indicate that these excited states are the same in character ( ππ ∗ ), but differ in the degree of electron delocalization between the benzene rings and the CO bond.

Time-resolved infrared and resonance Raman studies of benzil. Vibrational analysis and structures of the excited states

Structures of the S1 and T1 states of benzil are examined based on the experimental results from nanosecond time-resolved infrared spectroscopy and picosecond time-resolved Raman spectroscopy. Nanosecond time-resolved infrared spectra of the T1 state of benzil as well as its three isotopically substituted analogues were measured in carbon tetrachloride. The observed infrared bands of T1 benzil were assigned based on the frequency shifts on isotopic (18O, and deuteration) substitutions. The infrared band at 1312 cm−1 is assigned to the CO anti-symmetric stretch vibration. An infrared band that has large contribution from the central C–C stretch is not observed. Picosecond time-resolved resonance Raman spectra of the S1 state of benzil were also measured. It has been reported that after the photoexcitation, the benzil molecule shows an ultrafast conformational change in the S1 state. The observed resonance Raman bands are attributable to the vibrations of the relaxed form of the S1 state. By comparing the Raman and infrared spectra of the S0, S1, and T1 states of benzil, the structures of benzil in the excited states are discussed. Upon going from the S0 state to the S1 or T1 state, the bond order of the CO bond decreases while that of the central C–C bond increases. Although several ground-state bands appear in both the infrared and Raman spectra, there is no band observed simultaneously in the infrared and Raman spectra of the T1 state, except for bands attributable to the phenyl ring vibrations. We conclude that T1 benzil has the inversion center that arises from the trans-planar structure. The spectral pattern of the resonance Raman scattering of the relaxed S1 state is very similar to that of the T1 state. This implies that the molecular structure of the relaxed S1 state is similar to that of the T1 state. The structure of the relaxed form of the S1 state is also considered to be trans-planar.

Using picosecond and nanosecond time-resolved infrared spectroscopy for the investigation of excited states and reaction intermediates of inorganic systemsBased on the presentation given at Dalton Discussion No. 6, 9?11th September 2003, University of York, UK.

Time-resolved infrared (TRIR) spectroscopy, a combination of UV flash photolysis and fast infrared detection, is a powerful technique for probing excited states and detecting reaction intermediates. In this Perspective we highlight the application of TRIR to excited states by probing the nature of the lowest excited states of fac-[Re(CO)3(dppz-Cl2)(R)]n+ (R = Cl− (n = 0), py (n = 1) and 4-Me2N-py (n = 1); dppz-Cl2 = 11,12-dichlorodipyrido[3,2-a:2′,3′-c]phenazine) in CH3CN. The characterisation of [Cr(η6-C6H6)(CO)2Xe] and [Re(η5-C5H5)(CO)2(C2H6)] in supercritical Xe and liquid ethane solution exemplifies how this technique can be applied to detect new organometallic species.

Photoinduced Cl transfer reaction between biphenyl and carbon tetrachloride studied by nanosecond time-resolved infrared spectroscopy and picosecond time-resolved fluorescence spectroscopy

Photochemical reaction between biphenyl and carbon tetrachloride is studied with nanosecond time-resolved infrared spectroscopy and picosecond time-resolved fluorescence spectroscopy. Fluorescence lifetime of biphenyl in carbon tetrachloride solutions is measured with a picosecond time-resolved fluorescence spectrometer. The recorded lifetime is 3.8 ps, shorter than fluorescence lifetime in cyclohexane by a factor of four thousand. After the photoexcitation of biphenyl in carbon tetrachloride, the trichloromethyl (CCl 3) radical is formed as a reaction intermediate, which is confirmed by the detection of the radical's 896 cm −1 infrared band with nanosecond time-resolved infrared spectroscopy. One of the Cl atoms in solvent carbon tetrachloride is transferred to biphenyl to form the CCl 3 radical and a biphenyl–Cl adduct. Together with the already reported spectroscopic detection of the CCl 3 radical as an intermediate in photochemical reactions of trans-stilbene or anthracene with carbon tetrachloride, it is likely that this series of reactions are common for aromatic molecules.

Investigation of the photoisomerization of all- trans-retinal by singular-value-decomposition analysis of nanosecond time-resolved infrared spectra

Nanosecond time-resolved infrared spectroscopy has been used to study the photoisomerization of all- trans-retinal in cyclohexane. Singular-value-decomposition analysis of the observed time-resolved infrared spectra shows that three species are generated after the photoexcitation of all- trans-retinal. One is the “all-trans” triplet species, which exclusively relaxes back to the all-trans form in the ground state with a time constant of 5 μs. The other two are the 13-cis and 9-cis isomers in the ground state, which exhibit very rapid (<50 ns) production and no subsequent decay. These results suggest that the main pathway of 13-cis and 9-cis formation is via the singlet excited state and not via the triplet excited state. The quantum yields for all-trans to 13-cis and all-trans to 9-cis photoisomerization are estimated.

Structure of the Twisted-Intramolecular-Charge-Transfer Excited Singlet and Triplet States of 4-(Dimethylamino)benzonitrile As Studied by Nanosecond Time-Resolved Infrared Spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructure of the Twisted-Intramolecular-Charge-Transfer Excited Singlet and Triplet States of 4-(Dimethylamino)benzonitrile As Studied by Nanosecond Time-Resolved Infrared SpectroscopyMamoru Hashimoto and Hiro-o HamaguchiCite this: J. Phys. Chem. 1995, 99, 20, 7875–7877Publication Date (Print):May 1, 1995Publication History Published online1 May 2002Published inissue 1 May 1995https://doi.org/10.1021/j100020a008RIGHTS & PERMISSIONSArticle Views642Altmetric-Citations95LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (373 KB) Get e-Alerts

Nanosecond Time-Resolved Infrared Spectroscopy with a Dispersive Scanning Spectrometer

A nanosecond time-resolved infrared spectroscopic system based on a dispersive scanning spectrometer has been constructed. This is an advanced version of a similar system reported in a previous paper; the time resolution has been improved from 1 μs to 50 ns and the sensitivity from 10−4 in intensity changes to 10−6. These have been achieved by the use of a high-temperature ceramic infrared light source, a photovoltaic MCT detector, and a low-noise, wide-band preamplifier developed specifically for the present purpose. Time-resolved infrared spectra of a few samples of photochemical and photobiological interests are presented to show the capability of the system. The origin of the thermal artifacts, which have been found to hamper the time-resolved infrared measurements seriously, is shown to be due to the transient reflectance change induced by a small temperature jump. The future prospect of time-resolved infrared spectroscopy is discussed with reference to other methods including infrared laser spectroscopy and Fourier transform infrared spectroscopy.