Yingwu Tang

Correlations between solvatochromism, Lewis acid-base equilibrium and photochromism of an indoline spiropyran

The solvatochromism, Lewis acid-base equilibrium and photochromism of an indoline spiropyran in neat and mixed organic solvents were studied by UV-visible spectroscopy. The variation of the transition energy E T of the coloured form (PC) in different solvents was used as an empirical parameter to measure the polarity of the solvents and as a reference process to predict the shift of the Lewis acid-base equilibrium between PC and the colourless form (SP) and the thermal decolouration rates of the PC form in neat and mixed organic solvents. From the linearity of the plot of In K e or In k dc vs. E T , the Lewis acid-base equilibrium, photochromism and solvatochromism of the spiropyran were found to be similar solvent-dependent processes. The changes in K e and k dc were interpreted in terms of the differences in solvation of PC in solvents of different polarity. The relatively small influence of solvent polarity on the colouration rate k op serves as evidence supporting the view that the rate-determining ring-opening process is a concerted electrocyclic reaction.

Detailed investigation on a negative photochromic spiropyran

Abstract The negative photochromic properties of a spiropyran are investigated in various solvents and in solutions of different acidity. The results indicate that the polarity of the solvent has a prominent effect on λ max of the coloured merocyanine form (MC), whereas its effects on λ max of the closed form (SP) and on the coloration rates after visible bleaching are very weak. From the effect of acid concentration on the coloration rates the p K a of the cis intermediate Y in the coloration process is determined to be about 1.1 lower than that of the protonated merocyanine (MCH + ). The structures and configurations of MC, SP, MCH + and Y are assigned via their 1 H NMR spectra.

Complexation of phosphorus (III) with a novel tetrapyrrolic phthalocyanine-like macrocyclic compound

Abstract This contribution reports a detailed study of the complex formed by a novel phthalocyanine-like compound (2,9,16,23-tetraisopropoxy tetrabenzotriazacorrole) with phosphorus(III). The structure of this new tetrapyrrolic macrocycle (H[TBC(O i Pr) 4 P(OH)]) was identified by elemental analysis, conventional spectral measurements (FAB-MS, UV-Vis, IR, 1 H NMR, 13 C NMR, and 31 P NMR), as well as its chemical reactivities. The Q band in the electronic transition spectra of the complex lies at a wavelength of around 660 nm, which is slightly shorter than in the mother phthalocyanine. The ϵ of the Q band is approximately one half of the value of the sharp Soret band which exists at 450 nm. The unusual electronic transition spectra are interpreted as the molecular symmetry of the novel complex being reduced to C 1 or lower two-fold symmetry. Three chemically different species formed by protonation or/and deprotonation of the compound with acid and base were characterised and identified. In addition, the previously reported phosphorus(III) phthalocyanine [PcP III ] + is proposed to be H[TBCP(OH)] when compared with H[TBC(O i Pr) 4 P(OH)] in detail.

Photokinetic study on the photochromic reaction of Aberchrome 540TM: a further comment about the use of Aberchrome 540TM in chemical actinometry

Abstract The photochromic reaction of Aberchrome 540TM is studied using a photokinetic method. It is found that the photocyclization is accompanied by E↔Z isomerization. An equation is derived from photokinetic equations to describe the proportion of the light absorbed by the Z isomer to that absorbed by the E isomer. The value is 0.56 when the fulgide is irradiated after one cycle, which is the very reason why the irradiated solution should not be reused after bleaching.

Photokinetic study of a novel phenylfulgide: effects of solvents on its photochromic reaction

Abstract A photokinetic method was used to study the photochromic reaction of a novel fulgide, (E) -2-isopropylidene-3[1-3,4-dimethoxy-phenyl)ethylidene]-3-isopropylidene succinic anhydride. It was found that the photochromic reaction depends on the solvent polarity. The apparent ring-closure rate decreased with increasing solvent polarity, while the rate of E to Z isomerization increased. It was supposed that there were two kinds of conformation in the excited states. Increasing the solvent polarity favoured thr twisted conformation, which accelerated the E to Z photo isomerization, inhibiting the electrocyclilc reaction.

Degradation of rhodamine 6G in the peroxyoxalate chemiluminescent reaction

Abstract The degradation process of rhodamine 6G in the peroxyoxalate chemiluminescent system was monitored for the first time. A preferential degradation of rhodamine 6G dimers was suggested and identified spectroscopically. The influence of light irradiation or H 2 O 2 oxidation on dye degradation was insignificant according to our observations. The possible cause of rhodamine 6G degradation in the peroxyoxalate chemiluminescent system was discussed.

Influence of peptide bond on photosensitized oxidation of tryptophan, tyrosine and histidine dipeptides

IN photodynamic therapy, the damage of protein results from the photooxidation of one ormore of only five amino acid residues (tryptophanyl, tyrosyl, histidyl, methionyl and cys-teinyl). These five amino acids are also readily photooxidized in their monomeric states. How-ever, the reaction kinetics and mechanisms of free amino acids and bound amino acid residuesin proteins are somewhat different. For example, Tassin found that the incorporation of tryp-tophan into a peptide linkage dramatically altered its susceptibility to photooxidation as well as

UV-VIS spectroscopic study of the solvatochromism and chelating reaction of a benzothiazoline merocyanine in mixed solvents

Solvatochromism and chelating reaction of a benzothiazoline merocyanine are studied by UV-VIS spectra in DMF-H2O, DMF-1,4-dioxane and DMSO-1,4-dioxane. The effect of solvent polarity on UV-VIS absorption maxima and on equlibrium constant K of the chelating reaction is discussed. A linear correlation is obtained between lnK and ET.

A liquid photochromic diarylethene for high speed photo switches

A new photochromic diarylethene bears two chiral carbon atoms was designed and synthesized. This compound keeps in liquid state at room temperature which is the first example for 1,2-dithienylalkene derivatives to our knowledge. Owning to the liquid state, this compound undergoes a much faster reversible photochromic reaction than some 1,2-dithienylalkene derivatives in solid state, at ambient temperature. In addition, the fluorescence property and the uses of this compound in photo switches and non-reductive storage material were discussed.

Novel nondestructive readout method for rewritable storage systems of diarylethene photochromic molecules

1,2-bis(2-methyl-5-(4-methoxyl-phenyl)thiophene-3- yl)perfluorocyclopentene was synthesized by the elimination reaction of perfluorocyclopentene with butyllithium. The UV- Vis absorption spectra of both the open form and the closed form were detected. Their geometries were optimized by PM3 method, and ZINDO/S CI method was employed to calculate their UV-Vis absorption spectra, which were consistent with the experiments. Three fabricated dithienylethene derivatives linked by heterocyclic pyridinium betaines were investigated by the same methods to calculate their UV-Vis absorption spectra of both the open and closed forms. The results show that reading at the wavelength above 700 nm will not destroy the recorded information. Thus a non-destructive method is constructed on these diarylethene molecules.