Xinqi Song

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.

Investigation of the chelation of a photochromic spiropyran with Cu(II)

Abstract The formation of a Cu(II) chelate from a photochromic spiropyran in acetone in the dark and the decolouration of its coloured form and the Cu(II) chelate in tetrahydrofuran (THF) after UV irradiation were studied by UV-visible absorption spectroscopy. The results indicate that the rate-determining step of chelate formation in acetone is the formation of the coloured form. The concentration of metal ions has no effect. In THF after UV irradiation, the coloured form and its Cu(II) chelate are in equilibrium during thermal decolouration, with an equilibrium constant K of 8.9×104 l mol−1. The decolouration rate constants of the coloured form and its Cu(II) chelate are 1.57×10−2 s−1 and 5.7×10−4 s−1 respectively. From electron spin resonance (ESR) spectra of the chelate in acetone at 77 K, the structure of the chelate is square or square pyramidal.

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.

Novel chelation of photochromic spironaphthoxazines to divalent metal ions

Abstract The chelation properties of two photochromic spironaphthoxazine derivatives to divalent metal ions were studied in acetone. Two types of chelate can be observed in the absorption spectrum: an unstable chelate which is formed in the presence of Ni(NO3)2 or Co(NO3)2 on UV irradiation and may revert to the corresponding colourless form in the dark or by bleaching with visible light; the decolouration rate is decreased significantly compared with the metal-ion-free solution; a stable chelate with intense fluorescence emission, which cannot be bleached by visible light. From the influence of the structure of the spiro- oxazines and the nature and concentration of the metal ions and their counteranions on chelate formation, the structures of the two chelates and the mechanisms of the photoreaction and thermal reaction are discussed.

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.

Reinvestigation on the photoinduced aggregation behavior of photochromic spiropyrans in cyclohexane

Abstract Three photochromic spiropyrans (SP-1, SP-16, SP-4-SP) are investigated at carefully controlled condition. Special attentions are paid to the aggregation behavior and its effect on thermal decay of the colored form which is formed under UV irradiation. The three compounds show normal photochromism in CHCl 3 . In cyclohexane solution, the spectrum of colored form of SP-16 has structures in the visible region. Detail analysis indicates that its photoinduced merocyanine form cannot form aggregate and the structures of the spectrum are believed to come from the cis/trans isomers of merocyanine form. For SP-1 in cyclohexane solution, it is found that only the dimer is formed under N 2 laser irradiation at 8 °C, apart from the merocyanine monomer form. From E-diagrams and decoloration kinetics, it is known that only one linearly independent process exists in thermal decay of the colored form and there is an equilibrium between merocyanine monomer (B), colorless form (A) and the dimer (AB). In the decoloration process, the decoloration of B causes the shift of the equilibrium and which can further cause the dissociation of AB. This is the main route for the decoloration of AB. And all these results provide direct evidences that the composition of dimer is AB but not BB. From the effect of A concentration on the decoloration rate of the system, the formation constant (K) of AB is estimated to be 3.2 × 10 4 . For a bis-indolino-spirobenzopyran supramolecular system SP-4-SP, the result indicates that it can promote the formation of dimer and retard the decoloration of the dimer thus formed efficiently.

Study on phosphorus(III) complex of tetrabenzotriazacorrole : A novel phthalocyanine-like photosensitizer

Abstract The photosensitizing properties of a novel phthalocyanine analogue—hydrogen hydroxy-phosphorus(III)-2,9,16,23-tetraisopropxy tetrabenzotriazacorrole (H[TBC(O1Pr)4P(OH)] has been studied. Using diphenyl-isobenzofuran as chemical quencher, the photogeneration of singlet oxygen by H[TBC(O1Pr)4P(OH)] was identified together with its quantitative analysis. It is found that H[TBC(O1Pr)4P(OH)] is a more efficient single oxygen photosensitizer (θΔ =0.44, in N,N-dimethylformamide) than empty phthalocyanine H2Pc(O1Pr)4, and can be comparable to zinc phthalocyanine ZnPc(O1Pr)4. H[TBC(O1Pr)4P(OH)] can also effectively photo-generate the superoxide anion as shown by spin-trapping measurements. From the interpretation of the free energy changes ΔG ∗ in excited state electron transfer reactions, it is concluded that the superoxide anion is formed by electron transfer from the lowest excited singlet state (not the lowest excited triplet state) of H[TBC(O1Pr)4P(OH)] to oxygen. The results from confirm the presence of both Type I (radical) mechanism and Type II (single oxygen) mechanism in the H[TBC(O1Pr)4(OH)] photosensitized system.

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.