Kumao Hamanoue

Construction of a subpicosecond double-beam laser photolysis system utilizing a femtosecond Ti:sapphire oscillator and three Ti:sapphire amplifiers (a regenerative amplifier and two double passed linear amplifiers), and measurements of the transient absorption spectra by a pump-probe method

A double-beam Ti:sapphire laser photolysis system has been constructed for measurements of the subpicosecond transient absorption spectra by a pump-probe method. Although the spectroscopic characteristics tested for the practical availability are satisfactory enough, the transient absorption spectrum thus obtained exhibits an artificial time-dependent spectral change owing to the group velocity dispersion of the probing light pulse. Hence, its wavelength-dependent arrival time to the sample cell is determined utilizing the optical Kerr effect induced in carbon tetrachloride and the true transient absorption spectrum (the corrected spectrum) at a given delay-line setting is calculated by a microcomputer using a great number of uncorrected transient absorption spectra obtained at different delay-line settings. Interestingly, the corrected singlet-singlet absorption band (band C with a lifetime of 0.8 ps) obtained for the lowest excited singlet state of 9-nitroanthracene in cyclohexane really shifts with tim...

Implementation of an image intensifier coupled with a linear position‐sensitive detector for measurements of absorption and emission spectra from the nanosecond to millisecond time regime

Combining a nanosecond ruby laser with a detection system (a polychromator, an image intensifier and a linear position‐sensitive detector) controlled by a microcomputer, a convenient laser photolysis system has been constructed. Operating the image intensifier in gated or continuous mode, the time‐resolved absorption and emission spectra from the nanosecond to millisecond time regime can be recorded very easily by one or two excitation laser shots. The spectral resolution is 2.5 nm, while the shortest temporal resolution is 10 ns. Also, by simply turning a mirror in the polychromator, the multiple‐component decays of transient absorptions, fluorescences, and phosphorescences can be analyzed by means of a combination of a photomultiplier with an oscilloscope controlled by a microcomputer.

Phosphorescence spectra and triplet lifetimes of halogenoanthraquinones

Abstract Phosphorescence spectra and triplet lifetimes of anthraquinone and α-halogenoanthraquinones were studied in EPA at 77 K. It is suggested that the emitting states of α-halogenoanthraquinones are the lowest triplet states and that halogen substitution at the α position(s) in anthraquinone affects the electronic configuration of the lowest triplet states and their lifetimes.

The absorption kinetics of photoreductions of anthraquinone and 1-chloroanthraquinone by triethylamine in toluene and ethanol

Abstract The photoreduction of the title compounds by triethylamine in toluene and ethanol was found to originate via formation of an exciplex between the lowest triplet anthraquinones and triethylamine. This complex changed to a contact ion pair followed by proton transfer, generating anthrasemiquinone radicals and triethylamine radical.

The lowest triplet states of anthraquinone and chloroanthraquinones: The 1‐chloro, 2‐chloro, 1,5‐dichloro, and 1,8‐dichloro compounds

From the measurements of phosphorescence spectra and triplet–triplet absorptions of the title compounds, it has been proposed that the lowest triplet states (T1) of the α‐chloro compounds are of mixed nπ*–ππ* or ππ* character, while the nπ* triplet states are the lowest ones for anthraquinone and 2‐chloroanthraquinone (the β‐chloro compound). Compared with anthraquinone and the β‐chloro compound, much shorter lifetimes of the T1 states and small phosphorescence quantum yields were obtained for the α‐chloro compounds. These results have been interpreted in terms of the modification of the geometrical molecular structure by the interaction of the carbonyl group with chlorine atom(s) at the α position(s), causing the T1 states to be of ππ* character with short lifetimes.

Excimer formation of neat benzene derivatives studied by picosecond spectroscopy

Neat benzene, bromobenzene, and toluene were photolyzed by a 26 ps pulse of 347.2 nm light from a mode-locked ruby laser. Transient absorptions with λmax ≈ 515, 520 and 580 nm, respectively, were observed. It is suggested that biphotonic absorption of 347.2 nm light leads to higher energy states of benzene derivatives which give excimers.

Primary processes in the photoreduction of 1-chloro- and 1,8-dichloro-anthraquinones in ethanol studied by laser spectroscopy

Abstract The hydrogen-atom abstraction of the title compounds from ethanol was found to originate from the T 1 state in spite of the mixed nπ*-ππ* or ππ* character of the lowest triplet state (T 1 ). No evidence for electron transfer from ethanol to the T 1 state of α-halogenoanthraquinones was obtained.

Photoreductions of α-chloroanthraquinones followed by photochemical dehydrochlorination in ethanol at room temperature

Abstract In the 366 nm photolyses of α-chloroanthraquinones (the 1-chloro, 1,5-dichloro and 1,8-dichloro compounds) the absorption bands of the reactants and the products shifted to the blue and anthrahydroquinone was produced as the final product. Combined with the results of the 313 nm photolyses of α-chloroanthraquinones and those of the 450 nm or 465 nm photolyses of α-chloroanthrahydroquinones, the results of the 366 nm photolyses of α-chloroanthraquinones were interpreted in terms of the following consecutive reactions: 1,5-dichloroanthraquinone or 1,8-dichloroanthraquinone 1,5-dichloroanthrahydroquinone or 1,8-dichloroanthrahydroquinone 1-chloroanthraquinone 1-chloroanthrahydroquinone anthraquinone anthrahydroquinone. In the step involving the photoreduction of 1,8-dichloroanthraquinone, however, a novel phenomenon was observed: the photolysis gave rise to the formation of a precursor which disappeared by a dark reaction, following a first-order rate law, to yield both the reactant and the product (1,8-dichloroanthrahydroquinone) simultaneously. This precursor was assigned to a complex of two 1,8-dichloroanthrasemiquinone radicals. The photolysis of 2-chloroanthraquinone gave rise to the formation of 2-chloroanthrahydroquinone, and no dehydrochlorination was observed.

The excited state dynamics of triplet 1,8‐dichloroanthraquinone in solutions at room temperature

The transient absorption spectra of the title compound (1,8‐DCAQ) in solutions at room temperature have been measured by the picosecond laser photolysis, and the buildup and decay of a new absorption were observed on a picosecond time scale. The decay of this absorption was accompanied by a rate matching increase in the triplet–triplet absorption of the lowest triplet state of a ππ* character. Since the addition of 2,5‐dimethyl‐2,4‐hexadiene (1 M) or triethylamine (2 M), as a triplet energy acceptor, quenched the new absorption, it was assigned to the second nπ* triplet state of 1,8‐DCAQ with an intramolecular charge–transfer character between the chlorine and oxygen atoms.

Spectroscopic studies on the primary processes in the photoreduction of α-chloroanthraquinones in ethanol at room temperature

Abstract The hydrogen-atom abstraction of 1,5-dichloroanthraquinone in ethanol at room temperature was studied by picosecond and nanosecond laser photolysis. By combining these results with those previously obtained for 1-chloroanthraquinone and 1,8-dichloroanthraquinone, it was concluded that the picosecond laser photolysis gave the transient absorption spectra due to the second and/or lowest triplet states of α-chloroanthraquinones. Nanosecond laser photolysis revealed that the hydrogen-atom abstraction of α-chloroanthraquinones from ethanol originated from the T 1 state in spite of the mixed nπ*-π* or π* character of the lowest triplet state (T 1 ). The reactivity for the hydrogen-atom abstraction decreased with increasing π* character of the T 1 state.