Tunable photochromism of spirooxazines via metal coordination

Spiropyran-linked dipeptide forms supramolecular hydrogel with dual responses to light and to ligand-receptor interaction

Integration of photo-sensitive spiropyran with dipeptide d-Ala-d-Ala in one small molecule resulted in a hydrogelator which can form supramolecular hydrogel with responses not only to light but to ligand-receptor interaction.

Synthesis and Solid-State Photochromism of 1,3-Diphenyl-4- (2-chlorobenzal)-5-hydroxypyrazole 4-Methylthiosemicarbazone

A new photochromic compound containing a pyrazole-ring unit, 1,3-diphenyl-4-(2-chlorobenzal)-5-hydroxypyrazole 4-methylthiosemicarbazone, was synthesized. Its structure, photochromic properties, and photochemical kinetics were characterized. The results show that the title compound exhibits reversible enol-keto photoisomerization, excellent photostability, and high fatigue resistance. An intra- and intermolecular proton-transfer mechanism is proposed.

Inclusion complex of spironaphthoxazine with gamma-cyclodextrin and its photochromism study

An environmentally benign transparent photochromic film, 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]-naphtho[2,1-b][1,4]oxazine] (SPO) /gamma-cyclodextrin (gamma-CD), was prepared using the cast-coating method, and the nanocavity effect of gamma-CD on the photochromism of SPO was studied. The film mainly consists of the inclusion complex SPO@gamma-CD, which has been verified by EA, TGA, XRD, MS, and ICD to comprise a 1:1 host-guest stoichiometry. The film shows normal photochromism. The decoloration of photomerocyanine (PMC) fits biexponential decay: PMCs located in the cavity of gamma-CD decay with a rate constant of 6.0 x 10(-2) s(-1), which is nearly one order faster than those PMCs outside of the cavity.

Elucidating the Mechanisms of Acidochromic Spiropyran-Merocyanine Interconversion

The thermal and photochemical processes associated with the acid-induced conversions of 6-nitroBIPS, SP-1, to form the protonated merocyanine (MC-OH+) were investigated via UV/vis spectrophotometric studies in acetone. It was found that the mechanism of trifluoroacetic acid (TFA)-induced ring-opening of the SP and the rate of MC-OH+ formation follows a general acid catalysis mechanism. In accord with this mechanism, the thermal growth of the acid-induced ring-opened form (MC-OH+) was retarded as the concentration of TFA in the medium was increased. The N-protonated SP, i.e., SP-NH+, is formed in a competing side-equilibrium process as an unreactive "sink", with the nitrogen lone-pair no longer available to drive the ring-opening process and resulting in the inverse rate dependence as a linear 1/kobs vs [HA] plot. Addition of a tertiary amine to MC-OH+ regenerated MC which underwent thermal ring closure to the SP, thus restoring its function as a molecular switch. NMR titration of SP samples showed a downfield shift of the N-substituent peak upon increasing the TFA concentration. However, a saturation behavior could not be observed with SP-1 up to 1 M acid, unlike the model compound, N,N-dimethylaniline (N,N-DMA), which indicates a base strength order of N,N-DMA > SP-1. Further, we have demonstrated that in solvent acetone, on acidification, the normal photo- and thermochromic behavior is reversed; now MC-OH+ is photochemically transformed into SP-H+, which undergoes thermal ring-opening to MC-OH+.

Modulation of the Photochromic Property in an Organoboron-Based Diarylethene by a Fluoride Ion

Organoboron-based diarylethene was successfully synthesized and exhibited photochromic property. Furthermore, its photochromic property can be modulated by a fluoride ion. The absorption maximum of the photostationary state shifted from 655 to 490 nm upon addition of a fluoride ion. The modulation mechanism is attributed to the special Lewis acid-base interaction between a trivalent boron atom and a fluoride ion.

Copper Ion-Selective Fluorescent Sensor Based on the Inner Filter Effect Using a Spiropyran Derivative

A highly selective copper(II) ion fluorescent sensor has been designed based on the UV-visible absorption of a spiropyran derivative coupled with the use of a metal porphyrin operative on the fluorescence inner filter effect. Spiropyrans, which combine the characteristics of metal binding and signal transduction, have been widely utilized in cationic ion recognition by UV-visible spectroscopy. In the present work, the viability of converting the absorption signal of the spiropyran molecule into a fluorescence signal was explored. On account of overlap of the absorption band of the spiropyran (lambda(abs) = 547 nm) in the presence of copper ion with the Q-band of an added fluorophore, zinc meso-tetraphenylporphyrin (lambda(abs) = 556 nm), the effective light absorbed by the porphyrin and concomitantly the emitted light intensity vary as a result of varying absorption of the spiropyran via fluorescence inner filter effect. The metal binding characteristic of the spiropyran presents an excellent selectivity for copper ion in comparison with several other heavy or transition metal ions. Since the changes in the absorbance of the absorber translate into exponential changes in fluorescence of the fluorophore, the novelty of the present device is that the analytical signal is more sensitive over that of the absorptiometry or that of the fluorometry using one single dye. To realize a practical fluorescent sensor, both the absorber and fluorophore were immobilized in a plasticized poly(vinyl chloride) membrane, and the sensing characteristics of the membrane for copper ion were investigated. The sensor is useful for measuring Cu2+ at concentrations ranging from 7.5 x 10(-7) to 3.6 x 10(-5) M with a detection limit of 1.5 x 10(-7) M. The sensor is chemically reversible, the fluorescence was switched off by immersing the membrane in copper ion solution and switched on by washing it with EDTA solution.

Research Trends in Photochromism: Control of Photochromism in Rigid Polymer Matrices and other Advances

Photochromism is receiving increasing attention because of its current application in high value-added ophthalmic lenses and potential applications in data storage and molecular switching. The performance of photochromic dyes, such as spirooxazines, chromenes, and diarylethenes, in polymers is important because the above applications require the dyes to be in a host polymer. The dyes can be broadly divided into P (photo) and T (thermal) types depending on the availability of a thermal decolouration route. Current research themes for the two types are presented with an emphasis on a new method of manipulating switching speeds in polymer matrices.