A fluorescence switch based on a controllable photochromic naphthopyran group

A fluorescence switch based on photoisomerization of naphthopyran (NP) has been designed by employing 2-(pyridin-2-yl)-benzimidazole (BPI) and the naphthopyran containing two pyran rings (NP) as fluorescent dye and photochromic compound, respectively. The fluorescence switch of benzimidazole derivative can be modulated either by controlling the irradiation time of UV light or by adjusting the amount ratio of fluorescent benzimidazole derivative to photochromic naphthopyran in both solution and polymethyl methacrylate (PMMA) film. The experimental results indicated that the decrease of fluorescence intensity of benzimidazole derivative is attributed to the interaction of benzimidazole with naphthopyran.     

Synthesis, optical and thermal studies of dendritic architectures with chalcone surface groups

Dendritic architectures bearing three, six, and twelve chalcone units in the periphery are synthesized through convergent approaches. Absorption, emission, photoisomerization, and thermal properties of the chalcone-based dendritic architectures are also studied.     

Enantiodifferentiating photoisomerization of cyclooctene included and sensitized by benzoate modified β-cyclodextrin derivatives: switching of product chirality by solvent

Solvent effect upon asymmetric photosensitization has been investigated in the enantiodifferentiating photoisomerization of cyclooctene(1Z), sensitized by benzoate modified β-cyclodextrin derivatives bearing nitrogen, oxygen or sulfur substituents. The enantiomeric excess (ee) and E/Z ratio of reaction products were susceptible to the concentration of methanol in the aqueous solution, which could switch to the chirality of product unprecedentedly. Further investigation indicated that the conformation of the modified CDs in aqueous methanol solutions with 1Z were highly sensitive to both the substituent(s) on benzoate moiety of the modified CDs and the concentration of methanol. Solvent content represents a new versatile tool to efficiently manipulate the asymmetric photochemical reactions, in which the chirality of products can be switched by simply changing the methanol content of reaction solvent rather than synthesizing the antipodal sensitizers.     

Phase Gratings in Photoreactive Polymers:A Way to Optically Pumped Organic Lasers

Summary.  Poly-(4-vinylbenzyl-thiocyanate) (PVBT) was investigated as a photoreactive polymer which changes its refractive index upon UV irradiation as is required for the production of phase gratings. After UV irradiation, the refractive index of PVBT films increased from n_D ²⁰ = 1.629 to n_D ²⁰ = 1.660 (Δn = +0.031). The change in the refractive index resulted mainly from the photoinduced isomerization of thiocyanate (SCN) to isothiocyanate (NCS) groups. It was possible to modify irradiated PVBT with 1-naphthylmethyl amine which lead to a further increase of the refractive index. Both the isomerization and the modification were followed with FTIR spectroscopy. This modification of the irradiated zones also yields an advantageous stabilization of phase gratings enscribed in PVBT. The investigations were carried out in the realm of novel organic distributed feedback (DFB) lasers. Received August 22, 2000. Accepted September 22, 2000     

Ultrafast Investigation of Excited-State Dynamics in Trans-4-methoxyazobenzene Studied by Femtosecond Transient Absorption Spectroscopy

The ultrafast photoisomerization and excited-state dynamics of trans-4-methoxyazobenzene (trans-4-MAB) in solutions were investigated by femtosecond transient absorption spectroscopy and quantum chemistry calculations. After being excited to the S\begin{document}$_2$\end{document} state, the two-dimensional transient absorptions spectra show that cis-4-MAB is produced and witnessed by the permanent positive absorption in 400\begin{document}$-$\end{document}480 nm. Three decay components are determined to be 0.11, 1.4 and 2.9 ps in ethanol, and 0.16, 1.5 and 7.5 ps in ethylene glycol, respectively. The fast component is assigned to the internal conversion from the S\begin{document}$_2$\end{document} to S\begin{document}$_1$\end{document} state. The other relaxation pathways are correlated with the decay of the S\begin{document}$_1$\end{document} state via internal conversion and isomerization, and the vibrational cooling of the hot S\begin{document}$_0$\end{document} state of the cis-isomer. Comparing of the dynamics in different solvents, it is demonstrated that the photoisomerization pathway undergoes the inversion mechanism rather than the rotation mechanism.     

Reversible Photoisomerization of β-Methyl-β-Nitrostyrene: The Role of Triethylamine

The photolysis of trans-β-nitro-βmethylstyrene in acetonitrile solution gives the cisisomer with a quantum yield of 0.8. Addition of triethylamine to the system leads to a small decrease in the photoisomerization quantum yield and the appearance of a strong EPR signal. This signal remains for several hours at the end of the irradiation. It is demonstrated that the EPR signal is associated to an intermediary produced during the triethylamine catalyzed thermal back formation of the trans isomer. This intermediary bears an unpaired electron mostly associated to the nitro group and suggest that the thermal back reaction takes place by an initial electron transfer from the amine to the nitro group, leading to a long lived zwitterionic biradical.     

飞秒瞬态吸收光谱技术研究反式对氨基偶氮苯的超快激发态动力学 (cited: 1)

利用飞秒瞬态吸收光谱技术研究了反式对氨基偶氮苯(AAB)溶解在乙醇中的超快激发态动力学．当利用400 nm光激发分子到S₂态后,由S_{211102412相似文献}   

THE CYANIDE PHOTOISOMERIZATION IN ZINC HEXACYANOFERRATE (II) SUPPORTED ON TITANIUM DIOXIDE-SILICA GEL COMPOSITE: A MATRIX EFFECT

Abstract

Zinc hexacyanoferrates(II), ZnHCF, were supported on the surface of titanium(IV) oxide grafted on a silica gel surface, SiO₂/TiO₂. The adsorbed complex species SiO₂/TiO₂/ZnHCF was characterized by cyclic voltammetry, differential pulse polarography and Mössbauer spectroscopy. The pentacyanoferrate (II) species would also be formed by an isomerization of one of the cyano groups, which forms a Zn-CN-Fe bond. The effect of supporting electrolyte in the electrochemical behavior of cyanoferrates was investigated using modified carbon paste electrodes. The modified electrode exhibits a quasi-Nernstian response showing the involvement of alkaline metal cations in the electrochemical process. The electrode prepared with the composite ≡TiHCFZn also exhibits electrochemical behavior dependent on acetate anion concentration selectively.     

甲基橙偶氮染料掺杂聚乙烯醇薄膜的光存储特性研究

研究了甲基橙(MO)偶氮染料掺杂聚乙烯醇(PVA)薄膜的光致双折射和全息光存储特性.利用YAG激光二倍频(532nm)作为写入光,He-Ne激光(632.8nm)作为读出光,考察了不同染料浓度薄膜的光致双折射,探讨了光致双折射和泵浦光功率的关系,并实现了全息光存储.阐明了MO/PVA光存储的物理机制.     

Theoretical characterization of the thermodynamics of the photoisomerizations of ethylene and propylene

A number of structures which may play a role in the thermal and triplet photochemistry of ethylene and propylene are calculated using ab initio methods. The energies and other properties obtained from these ab initio calculations are employed to calculate the heats of formation of the structures using the bond additivity correction (BAC) method of Carl Melius. Generally, the heats of formation appear to be accurate to within several kilocalories per mole, even for the triplet states and transition states encountered in this study. A final analysis reaches the conclusion that the triplet-sensitized photochemistries of ethylene and propylene occur through the hot ground states of these materials rather than through their respective triplet states.