Ren Nakao

MNDO-PM3 MO studies on the thermal isomerization of photochromic 1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-indoline]

Abstract Semiempirical MNDO-PM3 quantum chemical calculations were carried out for the merocyanine-form isomers of 1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-indoline] to reveal the thermal back reaction of the photochromic spiropyran. The thermal cyclization mechanism was discussed on the basis of the potential barrier heights during the conformational changes between the merocyanine-form isomers.

Polymeric siloxanes with a substituent and the spirobenzopyran moiety: Effect of polar substituent on the photochromic properties

Oligomeric polysiloxanes having the spirobenzopyran moiety and various substituents were prepared. The polymers were photochromic; the color changed from colorless to red on UV irradiation and the color faded on visible irradiation or on standing in the dark. The thermal decoloration was depressed by the polar substituents. However, the effect of the bulky substituent, which had been observed in the rigid siloxane resins, was not detected. In the inorganic/organic hybrid siloxane gels, the silica/(spirobenzopyran-bonding polysiloxane) system and the (spirobenzopyran-bonding silica)/polysiloxane system, the thermal decoloration was also affected by the polar substituent introduced into the polysiloxane portion. The effect was larger in the first case than in the second. The result can be interpreted by the term of the preferential diffusion of polar spirobenzopyran to the vicinity of the polar substituents during the gelation.

Theoretical quantum chemical study of spironaphthoxazines and their merocyanines: Thermal ring-opening reaction and geometric isomerization

Abstract We calculate potential energy curves of isomerization in the ground state of spironaphthoxazines (SNO) and their merocyanines ( EZ , ZZ , EE and ZE ) by ab initio methods. We find that in the curves cleavage of the spiro-bond gives firstly cisoid- ZZ , followed by the two paths to the ZZ isomer by rotation of the central C–N single bond or to the ZE isomer by inversion at the nitrogen atom. There is an interconversion path between the resulting ZZ and ZE , through cisoid- ZE . In addition, ZZ and ZE have paths to EZ and EE , respectively, by rotation of the CC bond. We also discuss the photochromic process in terms of the behavior of the specific merocyanines involved in the process.

Electronic spectra of radical ions of cyclic polysilanes

The absorption spectra of the radical ions of cyclic polysilanes, (Me2Si)n, where n = 5, 6, and 7, formed by γ-irradiation have been recorded for rigid matrices at 77 K. The absorption maxima of radical anions of the cyclic polysilanes showed a red shift from 670 to 900 nm with increasing ring size. shows a broad single band at 720 nm, whereas shows two bands in the wavelength region from 500 to 1000 nm. A single peak is observed for at 900 nm. Ring-size reduction of the cyclic polysilanes with production of dimethylsilylene was not observed for the radical ions below 173 K, in sharp contrast to the behavior shown by the photoexcited states.

Reaction of phenyl(trimethylsilyl)silylene with chloromethanes; Insertion into the CCl bond and abstraction of chlorine and HCl

Abstract Photolysis of tris(trimethylsilyl)phenylsilane in chloromethanes, Cl n CX (4 - n ) , ( n = 1–4, X = H, alkyl, and Cl) produced phenyl(trimethylsilyl)silylene as a major intermediate, which afforded three types of products: 1,1-dichloro-1-phenyltrimethyldisilane via abstraction of two chlorine atoms, 1-alkyl-1-chloro-1-phenyltrimethyldisilane via insertion into the CCl bond, and 1-chloro-1-phenyl-2,2,2-trimethyldisilane via abstraction of HCl. Possible reaction mechanisms for the formation of these products were discussed based on initial formation of an 1,2-zwitterionic intermediate. A small amount of a radical-reaction product, 2-chloro-2-phenyl-hexamethyltrisilane, and a product considered to be a cyclohexadienyl derivative were detected in all cases as minor products.

A molecular orbital study on the reactivity of L-ascorbic acid towards OH radical

The reaction between L-ascorbic acid (AAH2) and OH radical has been investigated theoretically. The addition site on AAH2 and AAH– is found to be the olefinic carbon adjacent to the carbonyl group, with much more distinct selectivity for AAH–. Dehydration is found to occur readily not from the neutral ˙OH adduct AAH2OH˙, but from the anion adduct, AAHOH˙–, which leads to formation of the most probable key intermediate radical 17(ascorbate anion radical). The parent molecule of AAH2, triose reductone TRH2(2,3-dihydroxprop-2-enal), undergoes ˙OH addition and dehydration in a similar manner to AAH2. The addition site has been confirmed by comparison of MO energies for four possible transition states of the TRH2(ab initio and MNDO) and AAH2(MNDO) systems. The importance of the conjugate bases, AAH– and TRH–, for yielding the key radicals is suggested.

Synthesis and photochromic properties of spironaphth [1,2-b]oxazine containing a reactive substituent

Abstract Spironaphth[1,2-b]oxazines having either an allyl group or a 3-(diethoxymethylsilyl)propyl group on the N -atom of the indoline ring have been prepared, as potential substrates for photochromic materials. In addition to displaying the well-known photochromism between the closed and open forms, the present spirooxazines exhibit photochromism between two geometric isomers of the colored open form. This behavior provides the basis for a non-destructive read-out system having light-induced information memory.

γ-Ray induced reduction of acid chlorides with trichlorosilane

Abstract The γ-ray induced reduction of various acid chlorides (RCOCl) with trichlorosilane was studied at ambient temperature. Trichlorosilyl radicals were found to attack acid chloride selectively at chlorine atom to produce acyl radicals at the first step. The preference of chlorine-atom attack to carbonyl-oxygen-atom attack is explained in terms of molecular orbital calculations (STO-3G); the SOMO (singly occupied molecular orbital) of trichlorosilyl radicals is more likely to interact with the energetically closer σ-HOMO (C-Cl) than π-HOMO (CO) of acid chlorides. The acyl radicals thus formed yield two kinds of products depending on the nature of the alkyl moiety involved. When the alkyl moeity (R) is tertiary, the acyl radical undergoes decomposition into carbon monoxide and an alkyl radical which finally yields an alkane (RH). When R is primary, the acyl radical abstracts a hydrogen atom from trichlorosilane producing an aldehyde, which, by subsequent hydrosilation, gives an alkoxysilane (RCH2OSiCl3) as a final product. Thus, the present reaction can be used as a complementary synthesis to the reported method in which initiators are used.

MNDO-PM3 MO Studies on the Thermal Enantiomerization of 1′,3′,3′-Trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-Indoline]

Abstract Semiempirical MNDO-PM3 quantum chemical calculations were carried out for the isomers, stable and transition states, of the titled compound (Sp) to reveal the thermal enantiomerization of the photochromic spiropyran. To elucidate the mechanism in DMSO solution, COSMO calculations were carried out. Three possible conformations of photomerocyanines, EE, EZ, and ZE were optimized as planar, whereas ZZ isomer was not planar. Isomerization between EZ and ZZ and ring opening of Sp to ZZ were successfully calculated, while the other processes were prohibited. The mechanism for enantiomerization of (RS)-Sp was explained by a series of (R)-Sp to ZZ(R), ZZ(R) to ZZ(S), and ZZ(S) to (S)-Sp reactions.

γ-Ray- and UV-induced generation of methyl(phenyl)silylene and silene species from heptamethyl-2-phenyltrisilane

A benzene solution of heptamethyl-2-phenyltrisilane (1) has been irradiated with γ-rays in the presence of methanol. Hexamethyldisilane, methoxymethyl(phenyl)silane (2) and a 1-methoxytetramethyldisilanyl- and trimethylsilyl-substituted cyclohexadiene (3) were produced. The formation of 2 and 3 can be interpreted in terms of reactions of methanol with methyl(phenyl)silylene and a silicon–carbon double-bonded intermediate (silene), respectively. These intermediates are generated as follows. Benzene is first excited by γ-rays and by collisions the energy transfers to 1. Excited 1 decomposes to give methyl(phenyl)silylene or undergoes rearrangement to a silene intermediate as when 1 is excited by UV light. A kinetic study revealed that the energy transfer in the γ-irradiated system is the same as that in a UV-irradiated system.