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Mexoryl SX (terephthalylidene-3,3′-dicamphor-10,10′-disulfonic acid, Ecamsule) is a water-soluble UV-A absorber. The near-IR phosphorescence spectrum of singlet oxygen generated by photosensitization with Mexoryl SX was not observed in air-saturated water. On the other hand, the time-resolved near-IR phosphorescence spectrum was observed in oxygen-saturated phosphate buffer (pH 7.4). The quantum yield of the singlet oxygen generation (ΦΔ) was determined to be 0.0021 ± 0.0005. The ability of Mexoryl SX as a photosensitizer is quite low. The question arises as to the quite low ΦΔ value. No phosphorescence was detectable from Mexoryl SX in ethanol at 77 K. We elucidated the nature of the lowest excited triplet (T1) state of Mexoryl SX using a time-resolved EPR technique, because this technique is powerful for the study of short-lived and nonphosphorescent T1 molecules. The strong time-resolved EPR signals were observed. This fact shows that a considerable proportion of the lowest excited singlet (S1) state molecules undergoes intersystem crossing (ISC) to the T1 state and the deactivation process of the T1 state is mainly radiationless. The observed zero-filed splitting parameters, T1 lifetime, and S1 → T1 ISC anisotropy suggest that the T1 state can be regarded as a 3nπ*–3ππ* mixing state in character and the two unpaired electrons in the T1 state do not localize on (4-methylbenzylidene)camphor, a closely related component. Although the shorter T1 lifetime (47 ns) prevents T1 state quenching by ground-state oxygen, the 3nπ* character may contribute something to the low ΦΔ value.

Riboflavin (RF), a water-soluble vitamin B2, is an endogenous singlet oxygen photosensitizer in human skin and eye. Time profiles of the near-infrared phosphorescence of singlet oxygen generated by RF have been measured in the absence and presence of l-ascorbic acid (AA, vitamin C), 3-O-ethyl-l-ascorbic acid (3-EtAA) and Trolox (TX, a water-soluble analogue of vitamin E) in phosphate buffer (pH 6.8). These substances suppress the RF-photosensitized singlet oxygen generation. For example, the quantum yield of singlet oxygen generation is decreased to a third by adding 0.4 mmol dm^(−3) AA or TX (the concentration of dissolved oxygen in air-saturated water is 0.27 mmol dm^(−3)). AA and TX are more efficient suppressors of RF-photosensitized singlet oxygen generation than 3-EtAA. The bimolecular rate constants for quenching of the excited singlet and triplet states of RF by AA, 3-EtAA and TX have been determined through measurements of fluorescence and transient absorption. These measurements suggest that the observed suppression is due to the quenching of the excited singlet and triplet states of RF by AA, 3-EtAA and TX. The bimolecular rate constants for quenching of singlet oxygen by AA, 3-EtAA and TX were determined to be 1.8 × 10^8, 0.27 × 10^8, and 4.4 × 10^8 mol^(−1) dm^3 s^(−1), respectively.

Menthyl anthranilate (MA, tradename meradimate) is a UV-A absorber. The interactions of ground-state molecular oxygen with the long-lived triplet state of MA produce singlet oxygen through energy transfer. The quantum yield of singlet oxygen generation is 0.12 in air-saturated ethanol. Kinetic traces of the near-IR phosphorescence of singlet oxygen generated by MA-photosensitization have been measured in the absence and presence of Trolox (a water-soluble analogue of vitamin E and a quencher of singlet oxygen) and α-tocopherol (vitamin E, a natural antioxidant) in ethanol. Fluorescence and transient absorption measurements suggest that Trolox and α-tocopherol quench the lowest excited singlet and triplet states of MA. As a result, Trolox and α-tocopherol suppress MA-photosensitized singlet oxygen generation. Not only the quenching of singlet oxygen but also the suppression of singlet oxygen generation is the mechanism of antioxidant properties of Trolox and α-tocopherol for MA. The ability of α-tocopherol to suppress the MA-photosensitized singlet oxygen generation in isododecane, used as a solvent for an oil-soluble UV absorber, is close to that in ethanol. Suppression of sunscreen-photosensitized singlet oxygen generation is an important method for the formulation of safe cosmetic sunscreens.

Diethylhexyl 2,6-naphthalate (DEHN, tradename Corapan TQ) is used as a photostabilizer for a widely-used UV-A absorber, butylmethoxydibenzoylmethane (BMDBM). The photophysical properties of DEHN have been studied through measurements of the transient absorption, fluorescence, phosphorescence and EPR spectra in ethanol. The energy level of the lowest excited singlet state of DEHN is higher than that of BMDBM (enol form). The singlet-singlet energy transfer from BMDBM to DEHN is energetically unfavourable. The energy level of the lowest excited triplet (T1) state of DEHN is lower than that of BMDBM. It is probable that the mechanism of photostabilization of BMDBM by DEHN is the triplet-triplet energy transfer from BMDBM to DEHN. The observed phosphorescence spectrum, T1 lifetime and zero-field splitting parameters indicate that the T1 state of DEHN can be regarded mainly as a locally excited 3ππ* state within naphthalene. The sum of the quantum yields of fluorescence of DEHN (0.59 ± 0.09) and singlet oxygen generation by DEHN (0.44 ± 0.04) is almost unity in ethanol. About 60% of the UV energy absorbed by DEHN is released as fluorescence, while about 40% is used to produce the excited triplet state. The photoexcited states of 2-naphthoic acid have been studied for comparison.

Hexyl diethylaminohydroxybenzoylbenzoate (DHHB, Uvinul A Plus) is a photostable UV-A absorber. The photophysical properties of DHHB have been studied by obtaining the transient absorption, total emission, phosphorescence and electron paramagnetic resonance spectra. DHHB exhibits an intense phosphorescence in a hydrogen-bonding solvent (e.g., ethanol) at 77 K, whereas it is weakly phosphorescent in a non-hydrogen-bonding solvent (e.g., 3-methylpentane). The triplet-triplet absorption and EPR spectra for the lowest excited triplet state of DHHB were observed in ethanol, while they were not observed in 3-methylpentane. These results are explained by the proposal that in the benzophenone derivatives possessing an intramolecular hydrogen bond, intramolecular proton transfer is an efficient mechanism of the very fast radiationless decay from the excited singlet state. The energy level of the lowest excited triplet state of DHHB is higher than those of the most widely used UV-B absorbers, octyl methoxycinnamate (OMC) and octocrylene (OCR). DHHB may act as a triplet energy donor for OMC and OCR in the mixtures of UV-A and UV-B absorbers. The bimolecular rate constant for the quenching of singlet oxygen by DHHB was determined by measuring the near-IR phosphorescence of singlet oxygen. The photophysical properties of diethylaminohydroxybenzoylbenzoic acid (DHBA) have been studied for comparison. It is a closely related building block to assist in interpreting the observed data.

2-Ethylhexyl salicylate (EHS, octyl salicylate) and homomenthyl salicylate (HMS, homosalate) are UV-B absorbers used in cosmetic sunscreens. Diethylhexyl 2,6-naphthalate (DEHN, tradename Corapan TQ) used as a mildly effective photostabilizer for labile butylmethoxydibenzoylmethane, the most widely used UV-A absorber, is an efficient singlet oxygen photosensitizer with a high quantum yield of singlet oxygen generation ΦΔ = 0.44 in ethanol. The effects of EHS, HMS, l-ascorbic acid (AA, vitamin C), 3-O-ethyl-l-ascorbic acid (3-EtAA) and Trolox (TX, a water-soluble analogue of vitamin E) on DEHN-photosensitized singlet oxygen generation have been studied through measurements of time-resolved near-infrared phosphorescence in ethanol. These compounds suppress DEHN-photosensitized singlet oxygen generation. 40% of ΦΔ is decreased by adding 32 mmol dm-3 EHS or HMS. ΦΔ is decreased to a half by adding 3.0 mmol dm-3 TX. Fluorescence and transient absorption measurements suggest that the observed suppression is due to the quenching of the excited singlet state of DEHN by EHS, HMS, AA and 3-EtAA. These compounds do not quench the excited triplet state of DEHN. On the other hand, TX quenches both the excited singlet and triplet states of DEHN. It was shown that these UV-B absorbers have a novel characteristic as a suppressor of photosensitized singlet oxygen generation. Suppressing singlet oxygen generation is an important method for the prevention of skin damage. To the best of our knowledge, this is the first report on the suppression of photosensitized singlet oxygen generation by UV absorbing molecules.

The intermolecular triplet–triplet energy transfer from a photounstable UV-A absorber, 4-tert-butyl-4′-methoxydibenzoylmethane (BMDBM), to UV-B absorbers, 2-ethylhexyl 4-methoxycinnamate (octyl methoxycinnamate, OMC), octocrylene (OCR) and dioctyl 4-methoxybenzylidenemalonate (DOMBM) has been observed using a 355 nm laser excitation in rigid solutions at 77 K. The decay curves of the energy-donor phosphorescence in the presence of the UV-B absorbers deviate from the exponential decay at the initial stage of the decay. The Stern–Volmer formulation is not valid in rigid solutions because molecular diffusion is impossible. The experimental results indicate that the rate constant of triplet–triplet energy transfer from BMDBM to the UV-B absorbers, kT–T, decreases in the following order: kT–T (BMDBM–DOMBM)>kT–T (BMDBM–OMC)≥kT–T (BMDBM–OCR). The presence of DOMBM enhances the photostability of the widely used combination of UV-A and UV-B absorbers, BMDBM and OCR. The effects of the triplet–triplet energy transfer on the photostability of BMDBM are discussed.

Chitin, a polymer of N-acetyl-D-glucosamine (GlcNAc), functions as a major structural component in chitin-containing organism including crustaceans, insects and fungi. Recently, we reported that acidic chitinase (Chia) is highly expressed in mouse, chicken and pig stomach tissues and that it can digest chitin in the respective gastrointestinal tracts (GIT). In this study, we focus on major livestock and domestic animals and show that the levels of Chia mRNA in their stomach tissues are governed by the feeding behavior. Chia mRNA levels were significantly lower in the bovine (herbivores) and dog (carnivores) stomach than those in mouse, pig and chicken (omnivores). Consistent with the mRNA levels, Chia protein was very low in bovine stomach. In addition, the chitinolytic activity of E. coli-expressed bovine and dog Chia enzymes were moderately but significantly lower compared with those of the omnivorous Chia enzymes. Recombinant bovine and dog Chia enzymes can degrade chitin substrates under the artificial GIT conditions. Furthermore, genomes of some herbivorous animals such as rabbit and guinea pig do not contain functional Chia genes. These results indicate that feeding behavior affects Chia expression levels as well as chitinolytic activity of the enzyme, and determines chitin digestibility in the particular animals.

The excited states of UV-B absorbers, ethylhexyl triazone (EHT) and diethylhexylbutamido triazone (DBT), have been studied through measurements of UV absorption, fluorescence, phosphorescence, triplet-triplet absorption and electron paramagnetic resonance spectra in ethanol. The energy levels of the lowest excited singlet (S1) and triplet (T1) states and quantum yields of fluorescence and phosphorescence of EHT and DBT were determined. In ethanol at 77 K, the deactivation process of EHT and DBT is predominantly fluorescence, however, a significant portion of the S1 molecules undergoes intersystem crossing to the T1 state. The observed phosphorescence spectra, T1 lifetimes and zero-field splitting parameters suggest that the T1 state of EHT can be assigned to a locally excited (3)ππ* state within p-(N-methylamino)benzoic acid, while the T1 state of DBT can be assigned to a locally excited (3)ππ* state within p-(N-methylamino)benzoic acid or p-amino-N-methylbenzamide. The quantum yields of singlet oxygen generation by EHT and DBT were determined by time-resolved near-IR phosphorescence measurements in ethanol at room temperature. EHT and DBT did not exhibit significantly antioxidative properties by quenching singlet oxygen, in contrast to the study by Lhiaubet-Vallet et al.

The excited states of UV-B absorber (4-methylbenzylidene)camphor (MBC) have been studied through measurements of UV absorption, phosphorescence, triplet-triplet (T-T) absorption, and steady-state and time-resolved electron paramagnetic resonance spectra in ethanol. The energy level and lifetime of the lowest excited triplet (T(1)) state of MBC were determined. The energy level of the T(1) state of MBC is much lower than that of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The weak phosphorescence and strong time-resolved EPR signals, and T-T absorption band of MBC were observed. These facts suggest that the significant proportion of the lowest excited singlet (S(1)) molecules undergoes intersystem crossing to the T(1) state and the deactivation process from the T(1) state is predominantly radiationless. The quantum yields of singlet oxygen production by MBC determined by time-resolved near-IR luminescence measurements are 0.05 ± 0.01 and 0.06 ± 0.01 in ethanol and in acetonitrile, respectively. The photostability of MBC arises from the (3)ππ* character in the T(1) state. The zero-field splitting parameters in the T(1) state are D = 0.0901 cm(-1) and E = -0.0498 cm(-1). The sublevel preferentially populated by intersystem crossing is T(y) (y close to in-plane short axis and to the C═O direction).

We describe the use of a new video-laryngoscope (McGRATH® X-blade™, X-blade) in patients with difficult airways. We report four cases of difficult and failed tracheal intubation using a conventional Machintosh laryngoscope and McGRATH® MAC in which tracheal intubation was accomplished swiftly and easily using a newly designed videolaryngoscope, the X-blade. The whole glottis was easily visible (Cormack-Lehane grade 1) with the X-blade. X-blade also provided a good view of glottic opening in a patient with obesity. We believe that X-blade is useful in patients with difficult airways.

Triplet energy transfer (TET) is an important photostabilization process for organic UV absorbers, such as 4- tert -butyl-4′-methoxydibenzoylmethane (BM-DBM) and octyl methoxycinnamate (OMC). To characterize interactions between UV absorbers as TET the interactions between BM-DBM and OMC have been studied through measurements of EPR and time-resolved phosphorescence spectra. The EPR B min signals and the phosphorescence of OMC were observed through the selective excitation of BM-DBM at 365 nm in EtOH at 77 K. These results indicate that the intermolecular TET occurs from BM-DBM to OMC. This is the first report of the experimental evidence of the TET between the organic UV absorbers.

A pyogenic granuloma (PG) is a capillary hemangioma that usually occurs on the skin or in the oral cavity; it is rarely observed in the gastrointestinal tract. We herein describe a case of a 86-year-old woman who presented with anemia. Esophagogastroduodenoscopy and colonoscopy did not reveal any significant bleeding focus, but capsule endoscopy revealed a bleeding focus in the small intestine. We performed double-balloon enteroscopy and identified a 7-mm-diameter, reddish, subpedunculated, hemispheric polyp with a smooth surface in the small intestine, approximately 100 cm from the ileocecal valve. The polyp was surgically removed, and the histological findings were consistent with a diagnosis of PG.

The excited states of 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM) and 4-tert-butyl-4'-methoxydibenzoylpropane (BM-DBP), the model of the keto form of BM-DBM, have been studied through measurements of UV absorption, fluorescence, phosphorescence, and electron paramagnetic resonance spectra in ethanol at 77 K. The energy levels and lifetimes of the lowest excited triplet (T(1)) states of BM-DBP, dibenzoylpropane (DBP), the model of the keto form of dibenzoylmethane (DBM), and the keto and enol forms of BM-DBM and DBM were determined. The energy level of the T(1) state of the keto form is much higher than that of the enol form in BM-DBM. The effect of tautomerization on the T(1) lifetime is small in DBM but large in BM-DBM. The methoxy and tert-butyl groups play an important role in lengthening the T(1) lifetimes of BM-DBP and the keto form of BM-DBM. The nature of the T(1) states of the keto and enol forms of BM-DBM can be explained in terms of the mixing of the (3)npi* and (3)pipi* states. The observed energy levels and the lifetimes of the T(1) states of the UV absorbers provide a useful suggestion for designing more photostable UV absorbers.

The photodissociation dynamics of a hexaarylbiimidazole (HABI) derivative with two pyrenyl groups was investigated by time-resolved transient absorption spectroscopy and fluorescence measurements. Transient absorption spectroscopy revealed that photodissociation took place in the wide time region of

The lowest excited triplet (T 1 ) states of 2,2′-bipyridine (BPY), 6,6′-dimethyl-2,2′-bipyridine (DMBPY), 2,2′-biquinoline (BQ), 2-phenylpyridine (2-PPY), 3-phenylpyridine (3-PPY), 4-phenylpyridine (4-PPY), quinoline (QN) and isoquinoline (iso-QN) have been studied through measurements of the phosphorescence and EPR spectra in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF 6 ]) and in ethanol. BPY, DMBPY and BQ have the trans conformation in the ground (G) and T 1 states in [BMIM][PF 6 ] and in ethanol. Although only neutral forms of BPY, DMBPY, BQ and 4-PPY were observed in ethanol, their singly protonated cations were observed in [BMIM][PF 6 ] in the G and T 1 states. In the T 1 states, the solvent effects of [BMIM][PF 6 ] on the electron spin distributions of the aza-aromatics studied and their singly protonated cations are small.

Dynamics of the photodissociation process of a hexaarylbiimidazole derivative, 2,2′-di(ortho-chlorophenyl)-4,4′,5,5′-tetraphenylbiimidazole (o-Cl-HABI), in benzene solution was investigated by means of the femtosecond–nanosecond laser spectroscopy. The time evolution of the transient absorption of the lophyl radical, the product of the photodissociation, was biphasic with the faster and the slower time constants of 80 fs and 1.9 ps, respectively. The faster time constant was ascribable to the formation of the lophyl radical through the bond fission after the excitation, and the slower time constant may be attributed to the conformational change and/or vibrational cooling of nascent radicals.

The energy levels and lifetimes of the lowest excited triplet (T1) states of UV-B absorbers, 2-ethylhexyl salicylate (EHS) and homomenthyl salicylate (HMS), and their deprotonated anions (EHS(-) and HMS(-)) were determined through measurements of phosphorescence and electron paramagnetic resonance (EPR) spectra in rigid solutions at 77 K. The observed T1 energies of EHS and HMS are higher than those of butylmethoxydibenzoylmethane, the most widely used UV-A absorber, and octyl methoxycinnamate, the most widely used UV-B absorber. The T1 states of EHS, HMS, EHS(-) and HMS(-) were assigned to almost pure (3)ππ* state from the observed T1 lifetimes and zero-field splitting parameters. EHS and HMS with an intramolecular hydrogen bond show a photoinduced phosphorescence enhancement in ethanol at 77 K. The EPR signals of the T1 states of EHS and HMS also increase in intensity with UV-irradiation time (photoinduced EPR enhancement). The T1 lifetimes of EHS and HMS at room temperature were determined through triplet-triplet absorption measurements in ethanol. The quantum yields of singlet oxygen production by EHS and HMS were determined by using time-resolved near-IR phosphorescence.

Ultrafast pump-probe measurement was applied to investigate the excited state deactivation dynamics of bisimidazolyl radical, 1,4-bis-(4,5-diphenylimidazol-2-ylidene)cyclohexa-2,5-diene (BDPI-2Y). BDPI-2Y is non-fluorescent and the recovery of the ground state took place in the time scale of femtoseconds to picoseconds, indicating a direct ultrafast nonradiative decay from the excited state. Coherent intermolecular vibrations were also observed and the low-frequency mode at 150 cm−1 and 128 cm−1 had a phase shift of ∼ π compared to the mode at 290 cm−1.

The molecular alignment and thermal stability of the mixtures DA composed of two different kinds of Schiff base liquid-crystalline materials, D with an electron-donating –N(CH 3 ) 2 unit and A with an electron-withdrawing–NO 2 unit, were investigated by using DSC, POM, XRD, and FT-IR measurements. The mesophases of the mixtures DA were more stable and had wider temperature ranges than those of the individual compounds D and A . The mixture DA55 ( D : A =50:50 mol%) on cooling exhibited the most stable liquid-crystalline phases affording the highest T SI (119 °C), the widest temperature range of the smectic phase (46.4 °C) and the highest values of Δ S SI (26.1 J K −1 mol −1 ) among the mixtures DA examined. Based on the analysis of the XRD measurements and the temperature dependence on the FT-IR spectra, the molecular packing of the mixture DA55 was proposed to form a bilayer structure in the smectic A phase, in which the heading group of the compounds D and A overlapped partially. The induction of the smectic phase and the enhanced thermal stability for the mixtures DA would be caused by the intermolecular interaction between the electron donor and acceptor mesogens.

A novel photochromic hexaarylbiimidazole derivative with azobenzene moieties was synthesised and the molecular structure was determined by X-ray diffraction. The spectroscopic investigations for the photochromic behaviours revealed the presence of the independent four photochromic states, viz, triphenylimidazole dimers with trans- and cis-azobenzenes, and triphenylimidazolyl radicals with trans- and cis-azobenzenes.

Reaction of an iminophosphorane 2 bearing the Martin ligand with dimethyl acetylenedicarboxylate, followed by a ring opening reaction of a [2+2]-cycloadduct between them, gave the corresponding α-iminoalkylidenephosphorane 3, which was hydrolyzed to afford 1,2λ5-oxaphosphol-5(2H)-one 4. The structure of the novel five-membered ring compound 4 was established by X-ray crystallographic analysis. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:282–286, 2001

The lowest excited triplet (T1) state of the most widely used UV-B absorber, octyl methoxycinnamate (OMC), has been studied through measurements of phosphorescence and electron paramagnetic resonan...

The phosphorescence decay of a UV-A absorber, 4-tert-butyl-4'-methoxydibenzolymethane (BMDBM) has been observed following a 355 nm laser excitation in the absence and presence of UV-B absorbers, 2-ethylhexyl 4-methoxycinnamate (octyl methoxycinnamate, OMC) and octocrylene (OCR) in ethanol at 77 K. The lifetime of the lowest excited triplet (T1) state of BMDBM is significantly reduced in the presence of OMC and OCR. The observed quenching of BMDBM triplet by OMC and OCR suggests that the intermolecular triplet-triplet energy transfer occurs from BMDBM to OMC and OCR. The T1 state of OCR is nonphosphorescent or very weakly phosphorescent. However, we have shown that the energy level of the T1 state of OCR is lower than that of the enol form of BMDBM. Our methodology of energy-donor phosphorescence decay measurements can be applied to the study of the triplet-triplet energy transfer between UV absorbers even if the energy acceptor is nonphosphorescent. In addition, the delayed fluorescence of BMDBM due to triplet-triplet annihilation was observed in the BMDBM-OMC and BMDBM-OCR mixtures in ethanol at 77 K. Delayed fluorescence is one of the deactivation processes of the excited states of BMDBM under our experimental conditions.

Electron paramagnetic resonance (EPR) spectroscopy was employed to determine the lifetime and absolute concentration of singlet oxygen, O 2 ( 1 Δ g ), in the gas phase. O 2 ( 1 Δ g ) molecules were generated by gas-phase photosensitization with octafluoronaphthalene. The absolute concentration of O 2 ( 1 Δ g ) at total pressure of 0.3 Torr was estimated to be 3 × 10 −6 mol dm −3 at 305 K under our conditions using the ground-state oxygen molecule, O 2 ( 3 ∑ g - ), as a quantitative standard. The observed lifetime of O 2 ( 1 Δ g ) is 7 s at 0.6 Torr. This is the first report of the gas-phase lifetime of O 2 ( 1 Δ g ) observed by EPR.

The photophysical properties of menthyl anthranilate (MA), a UV-A absorber, have been studied through measurements of UV absorption, fluorescence, triplet-triplet absorption and time-resolved thermal lens in ethanol at room temperature and/or 77 K. The phosphorescence and time-resolved electron paramagnetic resonance spectra have also been observed in ethanol at 77 K. The energy levels of the lowest excited singlet (S(1)) state and triplet (T(1)) state were determined. The quantum yields of fluorescence, phosphorescence and S(1) → T(1) intersystem crossing (ISC) were also determined. From the data on the lifetime and quantum yield, the rate constants of the radiative decay, internal conversion and ISC of the excited states of MA were determined. The exceptionally high ISC quantum yield of MA shows that the deactivation processes of the S(1) state of MA are different from those of most UV absorbers such as cinnamate, salicylate, 2-hydroxybenzophenone, benzotriazole and dibenzoylmethane derivatives, where the internal conversion rates of the S(1) states are much faster than the ISC rates. The observed T(1) lifetime and zero-field splitting parameters suggest that the T(1) state of MA possesses almost pure (3)ππ* character.

The excited states of UV absorber, ethylhexyl methoxycrylene (EHMCR) have been studied through measurements of UV absorption, fluorescence, phosphorescence and electron paramagnetic resonance (EPR) spectra in ethanol. The energy levels of the lowest excited singlet (S1) and triplet (T1) states of EHMCR were determined. The energy levels of the S1 and T1 states of EHMCR are much lower than those of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The energy levels of the S1 and T1 states of EHMCR are lower than those of octyl methoxycinnamate. The weak phosphorescence and EPR B(min) signals were observed and the lifetime was estimated to be 93 ms. These facts suggest that the significant proportion of the S1 molecules undergoes intersystem crossing to the T1 state, and the deactivation process from the T1 state is predominantly radiationless. The photostability of EHMCR arises from the (3)ππ* character in the T1 state. The zero-field splitting (ZFS) parameter in the T1 state is D** = 0.113 cm(-1).

Dioctyl 4-methoxybenzylidenemalonate (DOMBM) is an effective stabilizer for photolabile 4-tert-butyl-4'-methoxydibenzoylmethane (BMDBM). DOMBM is superior to the most widely used UV-B absorber, octyl methoxycinnamate (OMC), at preserving its UV-B absorbance in the presence of BMDBM. The energy levels of the lowest excited singlet (S(1)) and triplet (T(1)) states of DOMBM were determined by measuring fluorescence and phosphorescence spectra in ethanol at 77 K. The energy level of the T(1) state of DOMBM is lower than that of BMDBM and is higher than that of OMC. The triplet-triplet energy transfer from BMDBM to DOMBM was demonstrated by measuring the electron paramagnetic resonance (EPR) and time-resolved phosphorescence spectra. The phosphorescence and EPR signals of DOMBM are too weak to be observed through the direct excitation in ethanol at 77 K. The phosphorescence spectrum was observed by using external heavy atom effects of ethyl iodide. The EPR spectrum was observed by using benzophenone as a triplet sensitizer. The fluorescence quantum yield of DOMBM is small in ethanol at room temperature. Only the fast component, due to the heat released from the excited state of DOMBM, was observed in the time-resolved thermal lensing experiments at room temperature. These results show that the quantum yield of the S(1) → T(1) intersystem crossing is negligible and the deactivation process is predominantly internal conversion to the ground state for DOMBM.

Reactions of an iminophosphorane bearing the Martin ligand with a ketone, an isothiocyanate, and an alkyne gave the corresponding cycloadducts, 1,3,2 u 5 -oxazaphosphetidine, 1,3,2 u 5 -diazaphosphetidine-4-thione, and 1,2 u 5 -azaphosphetine, respectively, while that with dimethyl acetylenedicarboxylate (DMAD) and successive hydrolysis afforded the 1,2 u 5 -oxaphosphole-(2 H )-one. Thermal reactions of the cycloadducts were also studied.

Phosphorescence spectra of nonphosphorescent or very weakly phosphorescent new UV absorbers, 2-methylphenyl cinnamate (MePC), 2-methylphenyl 4-methoxycinnamate (MePMC) and 2-methylphenyl 4-ethoxycinnamate (MePEC) have been observed by using external heavy atom effects of ethyl iodide in ethanol at 77 K. The lowest excited triplet (T(1)) energies of these new UV absorbers are lower than those of a widely used UV-A absorber, 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM), in both keto and enol forms. The intermolecular triplet-triplet energy transfer from photolabile BM-DBM to MePMC was observed by measuring the time-resolved phosphorescence spectra. Electron paramagnetic resonance spectra have been observed for the T(1) states of these new UV absorbers in ethanol at 77 K by using benzophenone as a triplet sensitizer. The observed T(1) lifetimes, zero-field splitting (ZFS) parameters and molecular orbital calculations of the ZFS parameters suggest that T(1) states of these new UV absorbers posses mainly (3)ππ* character. The deactivation processes of the lowest excited singlet (S(1)) states are predominantly fluorescence and internal conversion to the ground (G) states in MePMC and MePEC, while the main deactivation process of the S(1) state of MePC is internal conversion to the G state. The molar absorption coefficients of MePMC and MePEC in the UV-A and UV-B regions are larger than that of most widely used UV-B absorber, octyl methoxycinnamate.

A novel photochromic hexaarylbiimidazole with a bithienyl group as an extended π-conjugation unit was synthesized and the light-induced lophyl radical was found to be stabilized due to the delocalization of an unpaired electron, and to strongly absorb near-infrared light.

A new family of pi-conjugated delocalized biradical compound is developed. The solution of 1,4-bis(2,5-diphenylimidazol-4-ylidene)cyclohexa-2,5-diene shows the ESR signal consisting of a moderately broad unresolved line, Delta H(pp) approximately 1 mT, at room temperature. The presence of the thermal equilibrium between a triplet biradical state and a singlet state is confirmed by the ESR measurements, and the spin concentration is determined as 7.90 x 10(21) spin/mol at 300 K. The spin concentration can also be controlled by modifying the molecular planarity. Moreover, the unrestricted DFT/B3LYP calculations suggest the biradical character of the singlet ground state, and the modulation of the energy gap between the singlet state and the triplet state is investigated from the theoretical point of view. Controlling the equilibrium between a diamagnetic state and a paramagnetic state will provide significant progress in the field of biradical chemistry, and the materials with the biradical character in a ground state will lead to a novel development of molecular-based organic magnets.

Fluorescence, phosphorescence, and electron paramagnetic resonance spectra have been observed for the excited states of a new UV absorber, 2-methylphenyl 2-naphthoate (2-MPN), in ethanol at 77 K. T...

This study provides conclusive proof that the thermally excited open-shell state with biradical character is contributing to the ground state of a closed-shell molecule, tF-BDPI-2Y, where four hydrogen atoms at the central phenylene ring are substituted with four fluorine atoms of 1,4-bis-(4,5-diphenylimidazol-2-ylidene)cyclohexa-2,5-diene (BDPI-2Y). A small increase in the population of biradical species of tF-BDPI-2Y results in the formation of the dimer form by the radical recombination reaction. Controlling the equilibrium between a closed-shell diamagnetic-quinoid state and an open-shell paramagnetic-biradical state will provide significant progress in the field of pi-conjugated delocalized biradical chemistry.

Cycloaddition reaction of an iminophosphorane bearing the Martin ligand with an alkyne gave the first stable 1,2λ5-azaphosphetine, whose structure was determined by X-ray crystallographic analysis, and variable temperature NMR spectroscopy revealed the existence of equilibrium with the corresponding α-iminoalkylidenephosphorane.

The first demonstration of photoinduced surface relief grating formation using amorphous thin films composed of a radical dissociative photochromic compound, 2,2'-di(ortho-chlorophenyl)-4,4',5,5'-tetraphenylbiimidazole, show that mass transfer occurred from the UV-light-irradiated area to the shaded area by patterned light irradiation (365 nm).

A novel photochromic hexaarylbiimidazole with a bithienyl group as an extended pi-conjugation unit was synthesized and the light-induced lophyl radical was found to be stabilized due to the delocalization of an unpaired electron, and to strongly absorb near-infrared light.