Spirooxazine Research Articles

Photochromism of spirooxazines in mesoporous organosilica films

In order to increase the colourability and improve the mechanical properties of sol–gel photochromic films, we present an original strategy in which spirooxazine (SO) molecules are dispersed in mesoporous organized films using the impregnation technique. Two types of SO photochromic molecules are trapped in sol–gel matrices. The first one allows optimization of the chemical and steric interactions between SO molecules and the sol–gel matrix. The second one leads to fast photochromism as previously observed in soft hydrophobic sol–gel matrices and mesostructured silica composites. The pore accessibility into the matrix and environments for spirooxazine molecules are optimized in robust 3D-hexagonal mesoporous films containing high amounts of methyl groups at the pore surface. After impregnation by a spirooxazine solution, the photochromic response is only slightly slower when compared with mesostructured or soft sol–gel matrices, showing that methyl groups offer good environments for spirooxazines. Moreover, the molecular loading in films is easily adjustable in a large range using a multi-impregnation procedure and increasing the film thickness.

Novel Properties of Photochromic Spirooxazine Nanoparticles

AbstractThe nanoparticles of a spirooxazine (SPO) and its photomerocyanine (PMC) were prepared through the reprecipitation method. Two distinct features were observed. One is that the decaying lifetime for PMC nanoparticles was 600 times of that for the dispersed molecules, and the other is that the fluorescence intensity of SPO nanoparticles was enhanced by 240 times of that of the dispersed monomer.

Synthesis and switching properties of photochromic carbazole–spironaphthoxazine copolymer

A photochromic switching copolymer was synthesized by typical radical copolymerization of 2-(9H-carbazol-9-yl) ethyl methacrylate, a vinyl monomer having a spironaphthoxazine residue. It reversibly changed the fluorescent intensity by alternative irradiation with ultraviolet and visible light probably due to the photoinduced electron transfer (PET) between carbazoles and the open form of spirooxazine (SPO) moiety. By the observation of photoresponsive viscosity and conductivity changes, it was confirmed that the copolymer could exhibit excellent viscosity and conductivity switching behaviors.

Waterchromism of protonated photomerocyanine dye

The red protonated photomerocyanine (PMCH) of spirooxazine (SPO) experiences a stepwise color modulation from red to purple and ultimately blue upon gradual addition of water. Both UV–vis absorption spectra and thermal bleaching kinetics indicate that the blue solution differs from the open form of SPO, i.e., photomerocyanine (PMC), and computer assisted simulations show that the blue solution is a complex composed of one PMCH and two water molecules, which are connected through hydrogen bonds. Thus, water has a characteristic effect on PMCH, and this phenomenon is proposed as waterchromism.

Refractive index modulation in films containing single and dual chromophore system

Photochromic properties of polymer films containing spirooxazine (SP) and copolymer containing diazo chromophores (IZO) were investigated. The SP underwent photoisomerization under exposure to UV light yielding open forms of merocyanines manifested by strong absorption band at ca. 600 nm. The spectra of SP film in transparent polymer matrix, recorded for a single component and for a mixture with IZO copolymer, revealed sensitivity of the materials to UV and visible light. The ellipsometric measurements showed a distinct change of refractive index of the UV treated films on bleaching by exposure to the red and green light. Treatment of the film in two-beam coupling arrangement with 532 nm linearly polarized laser light confirmed the formation of diffraction grating. The study of photoizomerization was accompanied by quantum chemical calculations of spectral and nonlinear optical properties of spirooxazine and merocyanine forms.

Photoisomerization of Azobenzenes and Spirocompounds in Nematic and in Twisted Nematic Liquid Crystals

Samples of a nematic mixture of ZLI1132 and of a twisted nematic mixture composed of ZLI1132 and chiral inductor S811, including 1%-10% (w/w) 4-N,N-dimethylaminoazobenzene (DAB), (4'-nitro)-4-N,N-dimethylaminoazobenzene (NDAB), spiropyran (SP), or spirooxazine (SO) were irradiated to produce the photochromic transformation of the dopant. The changes in the system were monitored by time-resolved transmission spectroscopy, time-resolved birefringence, or polarized Raman scattering. The medium sensitivity of the kinetics and spectroscopy of some of the probes was used to derive information on polarity of the medium. In the systems studied, apart from the changes in absorption spectrum, great changes in birefringence can be photoinduced and the order of the nematic phase can be changed in either direction, depending on the dopant. The open form of SP can discriminate orientation polarity. Although the polarity parallel to the mesogenic director is similar to that for acetone, the perpendicular orientation has a polarity similar to acetonitrile. In agreement with this observation, the kinetics of the Z --> E isomerization of NDAB, oriented parallel to the mesogenic director, also experiences a polarity similar to that for acetone. The decay rate constant of the open form of SP displays a linear relationship between its Arrhenius parameters, which is universal in a great variety of homogeneous solvents, solvent mixtures, and liquid crystals, therefore validating the hypothesis that the same type of transformation is observed in all these cases, namely, the decay of the open form monomer. The dopants used have been proven to be adequate probes of bulklike properties in locally heterogeneous systems as liquid crystals.

Acidichromism in the Langmuir–Blodgett films of novel photochromic spiropyran and spirooxazine derivatives

Two novel photochromic spiropyran (SP) and spirooxazine (SO) derivatives without substituted long alkyl chains were synthesized. They can form stable Langmuir monolayers at the air–water interface and can be transferred to solid substrates successfully through vertical dipping as Z-type Langmuir–Blodgett (LB) films. LB films of both of the compounds showed typical photochromism. An additional acidichromism was found for the LB films. The LB film of SO turned red upon exposure to HCl gas. Consecutive exposure to NH3 gas caused the film to turn blue. The red colour and blue colour can be changed reversibly upon alternate exposure to HCl and NH3 gas. For the LB film of the SP derivative, due to the protection of the spiropyran by the substituted group, the acidichromism was not obvious in the initial exposure to the HCl and NH3 gases. However, after several repeated exposures to HCl and NH3 gas alternately, the acidichromism became obvious. This paper presents a new route for SO and SP LB films changing from the “spiro” form to the merocyanine form through acidichromism besides the well-known photochromic route of this system.

Molecular orientation in mixed LB films containing photochromic molecules

Orientation of photochromic molecules in mixed Langmuir-Blodgett (LB) films that were subjected to ultraviolet irradiation has been investigated by polarised spectroscopy. The photochromic molecules (spiropyran (SP) and spirooxazine (SO)) were incorporated as guests in matrices of arachidic acid (AA), poly (methyl methacrylate) (PMMA) and poly (isobutyl methacrylate) (PIBM). The films were deposited in the dark (dark-deposited) and also while the Langmuir film on the water surface was subjected to ultraviolet irradiation (UV-deposited). Orientation of the open form of the chromophores was strongly influenced by the nature of the matrix and by the presence or absence of ultraviolet irradiation. In the case of LB films formed from either chromophore and PIBM, the dipole moments of the open forms exhibited large tilt angles relative to the substrate normal for both the dark-deposited and UV-deposited films. With AA or PMMA as the matrix, the tilt angles were large for the dark-deposited films, but the UV-deposited films displayed considerably smaller tilt angles. The nature of the matrix species and its Langmuir film is suggested as the basis for interpreting the observations.

Photochromic effect and spatial light modulation in spiro-oxazine dye-doped polymeric films

A strong reversible photochromic phenomenon in spiro-oxazine (SO) dye-doped polyvinyl alcohol (PVA) films is reported. The absorption spectrum of the SO/PVA film shows an ultra-violet (UV) light induced isormerization process taking place between two molecular configurations, which correspond to the two characteristic absorption bands at 360 nm and 595 nm, respectively. The temporal behavior of this photo-isomerization process is investigated. The molecular absorption coefficients of SO1 to UV light and SO2 to the probe beam at 515 nm are found to be 1.2 cm 2/J and 6 × 10 −2cm 2/J, respectively. The life time of SO2 in the dark is about 38 s. Spatial light modulation and UV-to-visible image conversion using this photochromic film are demonstrated experimentally.