Photolysis of 1-benzyloxy-2-pyridone (BP) in some solvents gave benzaldehyde and 2pyridone as main products along with a small amount of benzyl alcohol. The results of triplet-quenching and -sensitization experiments (Fig.4, 5) show the photolysis to proceed preferentially through the excited singlet state.
To make clear the mechanism of the photolysis of BP, the deuterium isotope effect on the quantum yield for the disappearance of BP was evaluated by the use of 1-(benzyl-ce-d2-oxy)2-pyridone as a reactant. From the magnitude of the isotope effects at 313 nm (Table 4), the photolysis in polar solvents is considered to proceed mainly through the mechanism involving the intramolecular hydrogen abstraction and the cleavage of the N-O bond. The mechanism involving the homolysis of the N-O bond predominates in nonpolar solvents. The isotope effects at 254 nm (Table 5) imply that the homolytic cleavage of the N-O bond should be significant regardless of the nature of the solvent used. Analysis of the solvent effects both on the fluorescence behavior of BP (Table 3) and on the quantum yield (Table 4, 5) suggests that the photolysis occurs in competition with rotational isomerization about the N-O bond.

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Relative fluorescence yields (π_f^R) and wave nunibers of absorption maximum (ν_max) of 3, 3'-diethyl-2, 2'-thiacarbocyanine (C₂) and 3, 3'-dioctadecyl-2, 2'-thiacarbocyanine (C₁₈) were measured in water and alkanols. The measurements were also carried out for C₂ and C₁₈incorporated in micelles and liposomes in aqueous solutions. These dyes exhibit intense intramolecular twistings in the excited state which induce the radiationless relaxations of the excited electronic energy and reduce the fluorescence yield. π_f^R of these dyes was found to be higher in micelles and liposomes than in the solvents which had the same effective polarity with those in micelles and liposomes. By employing Oster-Nishijima equation, the value of π_f^R was correlated with the polarity and viscosity of environment at close vicinity of these dye molecules (micro polarity and viscosity). The rather higher values of π_f^R in micelles and liposomes were explained in terms of the lower micellar effective polarity and the higher micellar effective viscosity around the dye molecules. On the basis of these results, the higher sensitizing efficiencies of these dyes in micelles and liposomes than in aqueous bulk phase were explained.

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A microcomputer-controlled N₂ gas laser photolysis system has been used to elucidate the dynamic behavior in the excited state of poly(N-vinylcarbazole), poly[2-(9-carbazolyl)ethyl vinyl ether] and polyurethanes having trans-1, 2-di(9-carbazolyl)cyclobutane in N, N-dimethylformamide. Under the stringent optical arrangements, the excitation intensity dependences of the transmitted intensity of the exciting pulse, the fluorescence intensity and the T_n, T₁ absorbance were investigated, which were interpreted in terms of the intrapolymer S₁-S₁annihilation. On the basis of these results, the relation between the S₁-S₁ annihilation and polymer structure was examined and the states formed through the S₁-S₁ annihilation were proposed to be the ground and triplet states of carbazolyl chromophores. This S₁-S₁ annihilation was directly observed with a ps Nd³⁺: YAG laser-streak camera system. By the analysis of the results of ps studies, the mean rate of energy migration from chromophore to chromophore was estimated to be 10¹²S^-1 The results of the present work have been found to be useful for elucidating the laser-induced primary photoprocesses of polymers.

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There has been a continued interest in photophysical and photochemical processes of cinnamic acid and its derivatives in both liquid phase and solid state.
We have studied the cooperative action of the electronic effect of methoxyl substituent and topotactic assistance of polymethylene chain upon the intramolecular photocyclization (pseudodimerization)of polymethylene dicinnamates. The substituent perturbations to the excited electronic structures of cinnamic acids were also explored theoretically on the basis of the molecular orbital calculations by the CNDO/S-CI method.
The experiments of direct UV irradiation on dilute acetonitrile solutions containing polymethylene dicinnamates (n=2-6 and 10) have revealed a striking rate enhancement of polymethylene bis(3-methoxycinnamate)s (n=3-5) toward the intramolecular photocyclization. Stereochemical analyses of the photoproduct from the trimethylene 3-methoxy derivative have shown that the major product was β-truxinate as in the case of unsubstituted derivatives. In the case of tetramethylene series, the major photoproduct of 3-methoxy derivative remained g-truxinate, although unsubstituted one gave β-truxinate as a major photoproduct. The CNDO/S-CI calculations indicated that 3-methoxy perturbations have led the excited electronic structure of the lowest excited singlet state (S₁) to the intramolecular charge transfer from the aromatic portion to the vinylene moiety, and have shown that the methoxyl substituent effect upon the relative efficiency of photocyclization can be nicely interpreted in terms of the atomic odd electron densities of the cr-carbon to the carbonyl function in S₁ state.
From these results, it was concluded that the combined factors of electronic perturbation of 3-methoxyl substituent and topotactic assistance of polymethylene chain (n=3-5) contribute to gaining an advantage for the formation of the intramolecular exciplex and result in the exceptional photolability of poly methylene bis(3-methoxycinnamate)s.

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In order to determine the relative reaction rates of inserting NH (¹Δ) radicals into the different C-H bonds of 2-methylbutane, hydrogen azide has been photolyzed in 2-methylbutane solution at 5 and -72°C. The relative yields of the amines produced by the insertion of NH(¹Δ) radicals into the primary, secondary and tertiary C-H bonds were found to be 1.0: O.26: O.19 at 5°C and 1.0: 0.40: 0.33 at -72°C, respectively. Therefore, the relative reaction rates per bond are 1.0: 1.2: 1.7 at 5°C and 1.0: 1.8: 3.0 at -72°C, respectively, for the primary, secondary and tertiary C-H bonds.
Three conclusions were obtained from these experiments: 1) The fraction of the hydrogen atom-abstraction reaction of NH(¹Δ) radicals is negligibly small compared with the insertion reaction.2) The insertion reaction of NH(¹Δ) radicals seems to have an activation energy.3) Hydrogen azide forms a "cluster" in the alkane solution.

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The irradiation of dimethyl 2, 4-pyridinedicarboxylate [1] in methanol with 254 nm light brings about both ionic and radical type reactions: methoxylation at the 6-position, methylation at the 5- and 6-positions, and hydroxymethylation at the 6-position (Table 1). The effects of 1, 3-pentadiene (Fig.4) and added sulfuric acid (Fig.2) on the photoreactions indicate that methylation at the 5-position and hydroxymethylation at the 6-position originate from the singlet π^* state of the ester C=O and the excited singlet state of the non-protonated pyridine nucleus, respectively (Scheme 1). The concentration dependence (Fig.3) and the effects of triplet quenchers (Figs.4 and 5) reveal that methoxylation at the 6-position and methylation at the 6-position proceed via the singlet excimer and the excited triplet state of the protonated form, respectively (Scheme 1). Gamma-irradiation of [1] in acidic methanol solutions leads to methylation at the 5-and 6-positions and hydroxymethylation at the 6-position (Table 2).

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Irradiation of 4-methylquinoline N-oxide [4] or 2-cyanoquinoline N-oxide [1] in aqueous ethanol leads to the formation of either lactam [5 ] (Process I ) or 1, 3-benzoxazepine [2](Process II). In order to elucidate the reaction mechanism, the effect of such inorganic anions as SeCN-, I-, SCN- and Br- upon the photochemical isomerization of [1] and [4] in aqueous ethanol was examined. The following results were obtained. [1] Both photochemical isomerizations (Processes I and II) were quenched by the addition of inorganic anions with the formation of deoxygenation product [3]and [6] the quenching being more pronounced in the order of SeCN->I->SCN-vBr- which is the same order as the redox potential (Tables 1 and 2). More noticeable was that irradiation of [1] in the presence of I- brought about the liberation of iodine, while in the case of [4 ] such an iodine liberation was not observed. ( 2 ) Quantum yields for the photoreactions of [1] and [ 4 ] were determined as a function of the concentration of I-. The quantum yields of the formation of [2] and [5] (φ₂and φ₅) decreased and those of[3] and [6] (φ₃ and φ₆) increased as the concentration of Iincreased, whereas the quantum yields of the disapperance of [1 ] and [4] (φ₀ and φ₄) were independent of the concentration of I- (Figs.1 and 3). The lifetime of intermediate species responsible for the quenching was estimated, from the Stern-Volmer quenching constant, to be ca.1.4 ns in the case of [ 4] and ca.370 ns in the case of [ 1] (Figs.2 and 4). The experimental results were consistent with the previously proposed mechanism: Process I [4]→[ 5] occurs with the formation of hydrogen-bonded radical ion pair [4 a] from the Si state (Scheme 2) and Process II [ 1]→[2] proceeds via the Si state with the intervention of oxaziridine [ 1a] (Scheme 1). The photochemical isomerization of quinoline N-oxides in hydroxylic solvents is generally considered to proceed according to the mechanism as shown in Scheme 3.

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A dynamic study was made on the quenching of the emission of tris(2, 2'-bipyridine)ruthenium 10 (R²⁺) caused by the electron-transfer reaction to 1, 1'-dimethyl-4, 4'-bipyridinium (methylviologen, MV²⁺) in the presence of sodium dodecyl sulfate (SDS). The electron transfer was most enhanced in the premicellar region, i. e., in the region where the concentration of SDS is below its critical micelle concentration. The present study was performed to clarify the detailed aspects of this enhancement. The main conclusions are as follows: ( 1 ) two types of R²⁺-SDS aggregates are present in the premicellar region: a 1: 2 complex of the type ((R²⁺·2DS-)_n). where DS- is the dodecyl sulfate anion, and substrate-rich induced micelles (premicelles), the presence of which is induced by R²⁺; ( 2 ) the SDS concentration which gives the maximum enhancement of the electron transfer corresponds to the boundary SDS concentration at which (R²⁺·2DS-)_n-type complexes are reorganized into the substraterich induced micelles with increasing SDS concentration; ( 3 ) the formation of such micelles is induced by the addition of MV²⁺ to the R²⁺-SDS solution; and ( 4 ) the effective electron transfer occurs in the substrate-rich induced micelles, not in the (R²⁺·2DS-)_n-type complexes.

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Although 1, 2, 4, 5-tetracyanobenzene (TCNB) reacts with toluene upon irradiation through electron-transfer followed by proton-transfer to give substitution products, the TCNB-benzene system is photochemically stable under similar conditions owing to the lack of a proton source in the molecule. However, irradiation of phenanthrene and anthracene as well as benzene in the presence of TCNB in methanol gave the corresponding 1: 1: 1 addition-elimination products. Thus the TCNB-benzene-methanol system gave 2, 4, 5-tricyanobiphenyl, 5-tricyano-4'-methoxybiphenyl and 5, 6-dicyanophthalide together with the thermally reacted product, 1, 1-dimethoxy-3-amino-5, 6-dicyano-1 H-isoindole. Irradiation of the phenanthreneand anthracene-TCNB-methanol systems gave the corresponding 9-(2, 4, 5-tricyanophenyl)10-methoxy-9, 10-dihydro derivatives. As a possible mechanism the formation of radical cation-radical anion pair upon irradiation of the TCNB-aromatic system followed by coupling of the pair leading to a zwitterion to which methanol then adds to give the stereospecific 1: 1: 1 addition products is proposed.

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The photochemical behavior of five derivatives of 1-(4-biphenylyl)-ω-(benzoyloxy) alkanes, [1 a]-[ 1e], n=2-4, has been investigated. Derivatives with polymethylene chain length, n=2, cleave into 4-vinylbiphenyl [2 ] and benzoic acid on irradiation while derivatives with chain lengths, n=3 and 4 provide the rearranged products C 3 J. Quenching of the fluorescence and decrease of the product yield by the addition of triethylamine suggested the mechanism (Scheme 3) which involves an intramolecular electron transfer from an excited singlet of biphenyl to benzoyloxyl group and the successive intramolecular proton transfer and 8-cleavage or coupling of the biradical formed, resulting in the formation of [2] or [3 ]. Solvent effects on the quantum yields for the formation of the products revealed that polar solvents are essential for the reactions, while very high solvent polarity and alcoholic solvents reduce the yields owing to the stabilization of the radical-ion pair by solvation and hydrogen bonding. On the other hand, the introduction of a substituent (X) to the para position of phenyl ring of benzoyloxyl group was found to indicate that the solvent polarity, which provides the maximum product yield, shifts to higher polarity region with increasing electron-donating ability of the substituent (X=CN, f(ε) =0.2-0.4; X =H, f(ε) =0.42-0.47; X =OCH₃, f(ε)>O.42) and that the maximum quantum yield decreases in this order (φ10^-2: 3.7, 2.6, 0.3). It was concluded that the electronic states and the chemical reactivity of the intermediates closely correspond to the solvent polarity.

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Time-resolved fluorescence spectra of intact cells of red and blue-green algea, Porphyridium cruentum and Anacystics nidulans, were measured by means of a picosecond laser and a time-correlated photon counting system. Fluorescence spectra were observed successively from various pigments in the light harvesting system in the order of phycoerythrin (PE), phycocyanin (PC), allophycocyanin (APC) and chlorophyll a (Chla). The spectrum changes with time in the range of 0-400 ps in P. cruentum and of 0-1000 ps in A. nidulans. The time-resolved spectra were analyzed into components to obtain the rise and decay curve of each fluorescence component. The time behaviors of sequential fluorescence emissions from the pigment system can be interpreted with the decay kinetics of an exp (-2kt^1/2) type. The rate constants of the energy transfer show that the energy transfer takes place much faster in the red alga P. cruentum than in the blue-green alga A. nidulans, particularly in the PC→APC step. The results also indicate that a far-emitting APC (APC B etc) does not mediate a main energy transfer from phycobilisome to Chl a.

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A spectral change due to the photoisomerization of merocyanine (5-[2-(3-ethy1-2-benzothiazolylidene)ethylidene]-3-methy1-2-thioxo-4-thiazolidinone) was studied quantitatively by the use of a diode array spectrophotometer. The concentration ratio of the thermally unstable form B to the stable form A was determined to be --1/6 in dark and ?1 under the strong irradiation of visible light. The quantum yields, which were estimated to be O.2 to 0.3 in several solvents, showed little significant dependence on temperature or on added acids. The reverse process in dark was very rapid in alcohols and further accelerated by the addition of a small amount of proton-donating substances such as H₂O and HCl while the activation energies (15.2+0.3 kcal/mol in ethanol and 11±1 kcal/mol in cyclohexane) were not affected by 89such addition at all. The peculiar behavior of the thermalizing rate constant kr, in HClH₂O-Et0H system was discussed in term of cluster formation or of the microenvironmental inhomogeneity in H₂O-Et0H system.

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Polycyclic aromatic compounds are recently of much interest because of their expected physicochemical and biochemical properties. However, the wider-ranging studies on the nature of polycyclic aromatic compounds have been hampered partly because of the lack of the general and facile regioselective synthetic route to these compounds so far. The authors have developed a new method to synthesize benz[a]anthracene-7, 12-diones [ 3] by the photochemical reaction of 2-bromo-3-methoxy-1, 4-naphthoquinone [1 a] with 1, 1-diarylethylene [2]. Employing the reaction, the authors synthesized a large number of polycyclic aromatic compounds. This methodology provides us a general one-pot regioselective synthetic route to a variety of polycyclic aromatic compounds.

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Irradiation of α-halo ketone in non-degassed methanol gave a-methoxy ketone along with ketone. The reaction patterns were significantly influenced by the structure of α-halo ketone. Thus, 2-halo-1, 2-diphenylethanone and methyl α-bromophenylacetate underwent relatively smooth photomethanolysis, while a-bromoacetophen&rie gave acetophenone almost exclusively upon irradiation in methanol. Introduction of methoxyl group on ortho position ofabromoacetophenone caused dramatic change in its photochemical reactivity. For example, irradiation of 2, 5-dimethoxy-a-bromoacetophenone afforded the products arising from ionic species. The results are interpreted as follows: the photoexcited state of α-halo ketone decays by homolysis to a radical pair. The radical pair gives radical products or undergoes electron transfer to afford an ion pair, which then undergoes carbonium ion reactions. But only α-halo ketone bearing appropriate substituents to stabilize the radical pair and/or ion pair can give rise to ionic products.

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Irradiation of 1-bromo-2, 3-dichlorocyclohexane, obtained by addition of molecular chlorine to 3-bromocyclohexane, in the presence of triethylamine resulted in the debromochlorination affording 3-chlorocyclohexane in 50% yield. Unsymmetrical allylic bromides were shown to yield the allyl-migrated ally! chlorides minimally contaminated with isomers. Thus, cinnamyl bromide can be converted regiospecifically to a-phenylallyl chloride. In a similar manner, 2-butenyl bromide afforded 2-methylally1 chloride as a major product. This novel photoinduced reductive dehalogenation is relatively free from product isomerizations and superior to various reported synthetic methods for allyl halides.

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The [2+2] photocycloadditions of enol ethers [2 a-j] to 1-naphthonitrile [1] were investigated in detail from the stereochemical and kinetic points of view. With phenyl enol ethers [2 g-i], the cycloadducts [3 g-i] with the endo phenoxyl group were much more favorably formed than the "exo" adducts [4 g-i]. Such endo selectivities were not observed in the photocycloadditions of alkyl enol ethers [2 a-d], where both the endo and exo cyloadducts were formed in almost equal amounts. The photocycloadditions of the enol ethers C2 were commonly stereospecific irrespective of the endo-orientation selectivities. Although cis- or trans-1-ethoxy- and 1-phenoxypropenes gave the cycloadducts in almost quantitative yields, no photoreaction took place at all with 1-methoxy- and 1-phenoxy-2-methylpropenes.
The detection of exciplex emissions in some cases as well as kinetic analyses involving quantum-yield measurements and oxygen-quenching experiments demonstrate that [ 1 ]-[2a-j]exciplexes commonly intervene as an important intermediate in the mechanistic pathways of the photocycloadditions. Moreover, the rate constants for the process from the exciplexes to the cycloadducts were estimated to be commonly greater than 10⁸ s^-1 irrespective of the structure of the enol ethers. On the basis of these observations, the stereochemical features of the cycloadditions are discussed in terms of the Michl's theory for the exciplex formation, the crossing from an exciplex to a pericyclic minimum, and the decay from the pericyclic minimum to the ground state. t Photochemical Reactions of Aromatic Compounds. XXXVIII.

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The titanium(IV) chloride-catalyzed photoreaction has been carried on some sugar molecules. Under these reaction conditions, D-glucose [9] and D-galactose [12] underwent a selective bond cleavage at the C 5-C 6 position, producing the corresponding pentodialdose derivatives [10a]and[13], respectively. The reaction is considered to proceed through (1) isomerization to furanoside structure [15], (2) formation of a titanium chelate at the C 5 and C 6 hydroxyl groups [17], and (3) electron transfer within the chelate. The good selectivity of the reaction was rationalized by assuming the highest reactivity at the 1, 2-diol system including the primary hydroxyl group.

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A room light promoted the formation of metal-free phthalocyanine (H₂Pc) in the reaction of phthalonitrile with sodium alkoxide at elevated temperatures. Moreover, UV irradiation gave H₂Pc even at room temperature where no formation of H₂Pc was observed without light. The photochemical yields of H₂Pc were almost independent of the kind of alkali metals among Li, Na, and K. In both the thermal and photochemical reactions, the yields of H₂Pc in primary alcohols were better than those in secondary alcohols, and hardly any formation of H₂Pc in the tertiary alcohols was observed. The yield of H₂Pc in the photochemical reaction was reduced by introducing oxygen in a greater degree than that in the thermal reaction. Cu-, , Ni-, and Co-phthalocyanines (MPc) were also obtained by the photoreactions, but the yields of MPc's were only slightly better than those in the corresponding dark thermal reactions. The X-ray diffraction patterns of H₂Pc obtained by the photoreactions did not coincide with any of the well-known α-, β-, or γ-forms. However, the crystal forms of MPc's were determined to be the 8-form.

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The photochemical reactions of dimethyl mesoxalate (DMO) with olefinic compounds, such as 2, 3-dimethyl-2-butene [2 a], 2-methyl-2-butene [2 b], 2-methyl-1-propene [2 c], 2-butenes [2 d], 1-butene [2 e], cyclopentene [2 f], cyclohexene [2 g], cycloheptene [2 h], and cyclooctene [2 i] were investigated. The products from these reactions were 1: 1 adducts of DMO and alkenes [2 a]-[2 e]. The 1: 1 adducts involve unsaturated alcohols, unsaturated ethers, and oxetanes. The ratio of the products depends on alkenes used as shown in Table 1. Based on the experimental results using naphthalene (or isoprene) as a triplet quencher, it is assumed that unsaturated alcohols are produced via the excited singlet state of DMO, and unsaturated ethers and oxetanes are formed via the triplet state of DMO. The reaction products from DMO and cycloalkenes (1: 1 adducts) are unsaturated alcohols and oxetanes. The ratio of the products also depends on cycloalkenes used (Table 3). Kinetic experiments of DMO and [2 a] show that the quantum yield for the oxetane formation decreases rapidly as the concentration of [2 a] increases (Fig.1). From the dependence of the quantum yield for the formation of unsaturated alcohols on [2 a] and [2 h] concentrations, the ratio of the rate constants of elementary processes was calculated. Though the quantum yield for the product formation from DMO and [2 a]is similar with that of DMO and [2 h], Cc and kg. in the photoreaction of DMO and [2 h] are very small compared with that of DMO and [2 a].

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When the inclusion complexes of 1, 1, 6, 6-tetraphenyl-2, 4-hexadiyne-1, 6-diol [1 ] or 2, 5diphenylhydroquinone [ 2 ] were irradiated in solid state, efficient stereoselective cycloaddition reactions of the guest molecules were found. Irradiation in solid state of chalcone derivatives [ 3 ] included in [1]or [ 2 ] gave the syn-head-to-tail dimers [21] almost in quantitative yields. Similarly efficient stereoselective cycloaddition reactions took place in irradiation of 9-anthacenecarbaldehyde C 5 and 2-pyridone [6 b]included in[ 1], giving [4+4] cycloaddition products, [24] and [25], respectively.

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Irradiation of 9, 9'-dinitro-9, 9'-bifluorenyls [1a-c] and dl- and meso-1, 2-dinitro-1, 2-diphenylethane (dl-[Id] and meso-[1d]) in DMF with a high-pressure Hg lamp caused reductive elimination of the nitro groups via a radical chain (ERc) mechanism to give the corresponding olefins [2a-d] which in turn gave 9, 9'-bifluorenyls [3a-c] and phenanthrene [4], respectively, on further irradiation. The aliphatic vicinal dinitro compounds, 1, 1'dinitro-1, 1'-bicychohexyl [1e] and 2, 3-dinitro-2, 3-dimethylbutane [1f], did not photoreact in DMF or cyclohexane under similar reaction conditions.

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Photochemical reaction of styrene and a-methylstyrene with triethylamine gave 1: 1 adduct [2] and reduced products [3] and C 4D as main products. In hexane, [2]was obtained preferably while [3] and [4] were favored in acetonitrile. An addition of methanol did not affect the product formation in acetonitrile, but depressed the formation of [2] and enhanced the formation of [3 ] and [4] in hexane. The analysis of the products formed in the presence of methanol-d suggests that the styrene-triethylamine exciplex reacts with methanol at the p-position of styrene which is supposed to be nagatively charged. Furthermore, the styrene radical anion is effectively formed in acetonitrile. Scheme 1 is proposed as the reaction mechanism. Carbon dioxide did not react with the exciplex, but reacted with the radical anion effectively to afford carboxylic acids [5 ]-[8] (total quantum yield ca. O.3). Similar reactions with other styrene derivatives, i. e., β-methylstyrene, indene, and 1, 1-diphenylethylene, gave the corresponding carboxylic acids in total yields of 42, 69, and 43%, respectively. In the case of stilbene, methyl cinnamate, and cinnamonitrile, however, the acids were not detected and the reduction products were obtained, suggesting the formation of radical anion. Localization of a negative charge at the β-olefinic carbon atom seems to be essential for the formation of the carboxylic acids. t Photochemical Carboxylation. I.

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Upon irradiation, 4-phenyl-2-oxa-3-azabicyclo[3.2.O]heptadiene [3a] afforded 2-phenyl 1, 3-oxazepine [4 a] in 80% yield. In order to clarify the reaction mechanism, p-methoxyphenyl and p-cyanophenyl derivatives, [3 b] and [3 c], were investigated. Both [3b] and[3 c] gave 1, 3-oxazepines in 52 and 71% yield, respectively, on irradiation at room temperature. When p-methoxyphenyl derivative [3 b] was irradiated at 7°C in benzene, (Z )-3-(3-(pmethoxyphenyl)2 H-azirin-2-yl)propenal C6 bp was isolated in 46% yield in addition to 1, 3oxazepine (4 1)1 3-formylpyrrole 15 bp, and (E)-azirinylpropenal [7 b]. (Z)-Azirinylpropenal [6 a] was also obtained in 14% yield by the irradiation of [3 a] at -78°C. The formation of a nitrile ylide originating from the azirine intermediate [6 c] was observed on the irradiation of [3 c] at -196°C, although the primary product could not be directly detected. The reaction pathway leading to 1, 3-oxazepine was discussed based on these experimental results. In addition, X-ray crystallographic analysis of the 1, 3-oxazepine [4 c] is described in this report. t Organic Photochemistry.

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Cyclopentadienone dimer [2], 5, 6, 8, 9-tetraphenyltricyclo [5. 2. 1. 02. 6] deca-4, 8-diene-3, 10dione was synthesized by the Diels-Alder additional reaction of two molecules of hydroxycyclopentanone. Photochemical investigation showed that [2] gave a photocycloaddition product [3] in a low yield on UV irradiation. The low yield suggested the existence of an intermediate which is able to emit strong fluorescence in a visible region. The thermodynamical calculation showed that the energy difference between both ground states of the dimer [2] and the photocyloaddition product [3] was 62 kJ/mol.

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Kinetics of photoinduced graft copolymerization of methoxypolyethleneglycol methacrylate (SM) and 2-(dimethylamino)ethyl methacrylate (DAEM) onto brominated polyacrylonitrile (PANBr) was studied. The photo-graft copolymerization in a batch reactor was carried out, and the concentrations of SM, DAEM and graft polymer were followed experimentally. Quantum yield of the photolysi of PANBr, kinetic parameters for the graft polymerization of SM or DAEM onto PANBr, monomer reactivity ratio, and φ factor of the termination in the graft copolymerization of SM and DAEM were determined independently. Simulation of the graft copolymerization process was performed by substituting these parameters into the equations of the stationary state for photo-graft copolymerization.

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Polybutadiene with pendant p-substituted cinnamates was synthesized by lithiation of polybutadiene, followed by coupling with lithium 3-bromopropoxide and esterification with psubstituted cinnamoyl chlorides. The incoporated amount of the p-substituted cinnamate reached a maximum of 11 mol% and was controlled by regulating the amount of butyllithium added and the reation time. The glass transition temperature (Tg) of the obtained polymer increased with increasing amount of the cinnamate and was not influenced by the nature of the para-substituents of the cinnamate. The rate of photodimerization was measured after trans-cis isomerization reached an equilibrium. Electron-attractive para-substituents accelerated the photodimerization. The relationship between the observed rate constants and Hammett's constants was linear.
Electron attractive para-substituents seemed to increase the concentration of species in an excited state which caused the enhancement of the photodimerization and at the same time increased the Tg dependence of the photodimerization due to the interaction between the cinnamate group and the double bonds of polybutadiene. Films of blend polymers of polybutadiene having p-methoxy- or unsubstituted cinnamates and polybutadiene having pnitrocinnamate were irradiated in order to enhance intermolecular photodimerization. The photodimerization took place in high efficiency in the case of the polymer blends containing p-nitro- and p-methoxycinnamates. The highest degree ofthe intermolecular photodimerization was observed at 50/50 of the mixing ratio.

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Kinetic parameters for intra- and intermolecular photocrosslinking of cinnamoyl groups in poly[2-(cinnamoyloxy)ethyl methacrylate] (PCEMA) and in copolymer of CEMA with methyl methacrylate were determined in THF solutions irradiated with a high-pressure mercury lamp at 30°C. The formation of intra- and intermolecular crosslinking for PCEMA in degassed THF solutions was followed by the change in peak of GPC elution curves. The quantum yields for intra- and intermolecular crosslinking formation calculated from the initial concentration dependence of the rate of cyclodimer formation of cinnamoyl groups in PCEMA by spectrophotometric measurements are φ_D^intra =1.9 × 10^-3 and φ_D^intra=0, respectively. From the data of the change in weight-average molecular weights by light-scattering measurements, φ_D^intra and the ratioφ_D^inter/(φ_D^inter+φ_D^intra) at various concentrations of polymers are determined to be 1×10^-6-4× 10^-5and 5×10^-4-2× 10^-2, respectively, and the effective concentration of cinnamoyl groups for intramolecular reaction in polymer chains is supposed to be C_eff=O.63 mol·dm^-3. Intermolecular crosslinking proceeds exclusively in very dilute solutions of PCEMA and P(CEMA-co-MMA), and φ_D^intra increases with increasing cinnamoyl contents in the copolymers. '

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In order to improve the intrinsic and the spectral sensitivities of the practical photo- ?initiated polymerization system, the photopolymerizations of multifunctional methacrylate or acrylate in a coated layer were carried out using a combination of sensitizers with radical precursors having a weak covalent bond in molecule, such as 3-phenyl-5-isoxazolone (PIO), 2, 4, 6-tris(trichloromethyl)-1, 3, 5-triazine (TCT) and 2-mercaptobenzimidazole (MBIm). PIO photochemically cleaves to give 2, 5-diphenylpyrazine on photoirradiation in hexane solution without sensitizer and decomposes thermally to give benzonitrile. The photosensitivity for the polymerization of pentaerythritol trimethacrylate using the benzanthrone (BA)-PIO system as a combined initiator reached 0.5 mJ/cm².
The effective photosensitive composition for argon-ion laser with good storage stability is obtained from a suitable combination of merocyanine dyes having absorption wavelength up to 490 nm with polyhalomethyl compound or sulfonyl chloride as radical precursors. For example, argon-ion laser sensitometry for photopolymerizable composition including the 3, 3'-carbonyl bis[7-dimethylaminocoumarin](BC)-TCT initiator system indicates that the minimum energy necessary for image formation is 0.6 mJ/cm².
A specific combination of 9-phenylacridine (9-PA) with certain heteroaromatic thiols such as MBIm gives high photosensitive composition in the polymerization of pentaerythritol tetraacrylate. Its photosensitivity is measured to be 0.3 mJ/cm², much higher than that obtained from the Michler's ketone/benzophenone combination.
From the photochemical and spectroscopic investigations of sensitizer/radical precursor combinations, the sensitization of the photoinitiated polymerization is assumed to be initiated by radicals produced through electron transfer (in the case of PIO) or energy transfer (MBIm) from the sensitizers to the radical precursors. The sensitization process in the TCTsensitizer systems appears to be more competitive and complex.

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Photochemical reactions of poly(phenyl methacrylate) (PPMA), acetylated poly(hydroxystyrene)(AcPHS) and poly(oxycarbonyloxy-1, 4-phenyleneisopropylidene-1, 4-phenylene) (PC)were investigated by using spectroscopic techniques and by studying the model reactions. When PPMA was exposed to deep UV radiation, it underwent photo-Fries rearrangement, which was confirmed by the appearance of two absorptions assigned to o- and p-hydroxy phenone moieties. The reaction products of phenyl acetate, considered as a model compound of PPMA and AcPHS, were identified by GC as a 2: 1 mixture of o- and p-hydroxyacetophenones. By comparing the changes of the IR spectra of PPMA with those of the model reaction, it was found that the reactivities at the o- and p-positions were almost the same in terms of the rearrangement of PPMA. In addition, the rearrangement tended to saturate as the reaction proceeded. The phenomenon may be ascribed to the photo-shielding effect due to the rearranged structures which have higher absorption coefficients than the PPMA repeating unit. AcPHS also underwent the rearrangement like the other aryl acrylate polymers. PC underwent photo-Fries rearrangement and main chain scission resulting from decarboxylation.
The reaction products of diphenyl carbonate, which was a model compound of PC, were examined using GC-MS in order to investigate the rearranged structures of PC and other structures.206The p1oducts contained phenol and a 26 1 mixture of dihydroxybenzophenone derivatives and hydroxybenzoate derivatives. The results showed that the dihydroxybenzophenone structures were a more likely candidate for the rearranged structures than the hydroxybenzoate structures. The diphenyl carbonate structure is considered to rearrange first to the phenyl hydroxybenzoate structures and subsequently undergo rearrangement to produce the dihydroxybenzophenone structures, since the phenyl hydroxybenzoate structures have much higher ?absorption coefficients than the diphenyl carbonate structure. The phenolic structure seemed to be the most likely ending group resulting from the main chain scission.

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The polymers with pendant p-(2-benzoylvinyl)cinnamoyloxy (PBVC) group were synthesized by the reaction of poly(1-chloro-2-epoxypropane) or poly(chloromethylstyrene) with potassium salt of p-(2-benzoylvinyl)cinnamic acid in an aprotic polar solvent. The polymers with pendant cinnamoyloxy (CIN) or p-(2-benzoylvinyl)berizoyloxy (PBVB) group were also prepared by the reactions of the polymers with the corresponding salts in an aprotic polar solvent or by phase transfer catalysis. It was found in measuring photochemical reactivity and practical photosensitivity that the polymers with pendant PBVC group have higher photochemical reactivity and practical photosensitivity than the polymers with pendant CIN or PBVB group.

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