摘要:

The first absorption bands of the tetramethyl polyenyl cations were calculated by the Pariser-Parr-Pople molecular orbital method. By considering the extraordinary hyperconjugation effect of methyl substituents and using the new-y, the calculated absorption wavelengths reproduce well the observed ones.

ISSN:1058-725X    

DOI:10.1080/10587250008023896

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Density functional calculations (B3LYP/6–31G*) have been carried out to investigate the transition state structure for the inversion mechanism in the thermalcis-transisomerization reaction of azobenzene and 4-amino-4′-nitroazobenzene. Four and eight conformations were optimized in order to find the inversion transition state of azobenzene and 4-amino-4′-nitroazobenzene, respectively. As a result, it is found that azobenzene and 4-amino-4′-nitroazobenzene have only one genuine inversion transition state, respectively. The inversion barrier of 4-amino-4′-nitroazobenzene is smaller than that of azobenzene. The dipole moment of the inversion transition state of 4-amino-4′-nitroazobenzene is extremely large compared to those of thecisandtransstructures.

ISSN:1058-725X    

DOI:10.1080/10587250008023897

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

ab initioand semi-empirical geometry optimization in conjunction with modified CS-INDO-CIPSI calculations was performed to predict the λmaxof absorption of merocyanines forms of spiro[indoline-naphthoxazine], spiro[indoline-naphthopyran] and diarylnaphthopyrans. The predicted λmaxare found in excellent agreement with experimental values providing the geometry used for vertical energies calculation is delocalized, i.e. obtained at the UHF/AM1 and DFT levels.

ISSN:1058-725X    

DOI:10.1080/10587250008023898

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Geometries of 3-Furyl, 3-pyrryl, 3-thienyl fulgides, and substituted 3-furyl fulgides were fully optimized at HF/6–31G and 6–31G* levels. It was found that theC-isomers of 3-furyl and 3-thienyl fulgides are more stable than theE-isomers, while theE- andC-isomers are isoenergetic in 3-pyryl fulgide. The activation energy of thermal ring-closing reaction for 3-furyl fulgide was estimated to be 21 kcal/mol. The electron donating groups enhance the bonding character between atoms to form the single bond in theC-isomer.

ISSN:1058-725X    

DOI:10.1080/10587250008023899

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Theoretical investigations were carried out on a series of spirooxazines which are known to exhibit photochromism. The calculational results obtained using polarization-propagator basedab-initiomethods give fairly good qualitative predictions of the absorption maxima for this series of spirooxazines, however, the predicted shifts of the absorption maximum down the series is in the opposite direction of the experimental measurements. This is discussed.

ISSN:1058-725X    

DOI:10.1080/10587250008023900

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

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.

ISSN:1058-725X    

DOI:10.1080/10587250008023901

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The application of Windows 95/98/NT for PPP MO (Pariser-Parr-Pople molecular orbital) calculation was developed by using the Inprise C++ builder. The novel two-center electron repulsion integral (new-γ), the concept of spectrochemical softness parameterkrsfor PPP calculation, was introduced in this application. The user can perform quickly the modeling of π-conjugated compounds on a PC monitor and select many suitable parameters (for example, ionization potentials, resonance integralsetc.) for the PPP calculation. The SCF calculation was momentarily performed and oscillator strength and LCAO coefficients of HOMO, LUMO or others were displayed. The calculations gave satisfactory results for the prediction of the electronic absorption spectra of polycyclic aromatic hydrocarbons(PAHs), symmetric cyanins and so on.

ISSN:1058-725X    

DOI:10.1080/10587250008023902

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effect on the quantum yield for the cyclization reaction and the circular dichroism (CD) spectral change by the addition of β-cyclodextrin (β-CDx) to an aqueous solution of 2,2′-dimethyl-3,3′-(perfluorocyclopentene-1,2-diyl)bis-(benzo[b]thiophene-6-ammonium)iodide (1a) were studied. The quantum yield for the cyclization reaction was increased because of the increase of the ratio of the photoactive anti-parallel conformation. The CD spectral change upon irradiation with 313 nm light was also studied. The induced CD spectrum of an aqueous mixture of1and β-CDx changed from negative to positive by 313 nm light irradiation and the CD spectral change was photoreversible.

ISSN:1058-725X    

DOI:10.1080/10587250008023903

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effect of hydrogen bonding on the photochemical cis-trans isomerization is discussed on the basis of the results of absorption and fluorescence spectra as well as of the determination for the efficiencies of photochemical and photophysical processes.

ISSN:1058-725X    

DOI:10.1080/10587250008023904

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The molecular area of an amphiphilic azobenzene (AZ) bearing a carboxylic group was larger on aqueous subphase containing polyallylamine (PAA) than on the subphase containing Cd2+. In AZ/PAA LB films, AZ was deprotonated and PAA was protonated, indicating the salt formation of the two components. When the AZ/PAA LB films were stored in the dark, the absorption spectra of the LB films changed due to the variations in the orientation and the electronic structure of AZ. The LB films of AZ/Cd2+showed similar structural changes and, in the final state, took almost the same structures with those of AZ/PAA LB films although the initial structures were different. AZ showed reversible photoisomerization in the AZ/PAA-LB films both in the initial and the saturated state. Photoisomerization of AZ did not proceed in the AZ/Cd2+LB films either of the initial and the saturated state probably due to the lack in free volume.

ISSN:1058-725X    

DOI:10.1080/10587250008023905

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor