Photoinduced Volume Research Articles

Highly Sensitive Photopolymer for Holographic Data Storage Containing Methacryl Polyhedral Oligomeric Silsesquioxane.

Herein, via introducing eight methacryl polyhedral oligomeric silsesquioxane (Ma-POSS), we dramatically enhance the holographic performance of phenanthraquinone-doped poly(methyl methacrylate) (PQ/PMMA) photopolymer with excellent characteristics of high sensitivity, high diffraction efficiency, and neglectable volume shrinkage for holographic data storage, the photosensitivity, diffraction efficiency, and volume shrinkage reaching 1.47 cm/J, ∼75%, and ∼0.09%, respectively. Ma-POSS here dramatically enhances the photosensitivity ∼5.5 times, diffraction efficiency more than 50%, and suppressed the volume shrinkage over 4 times. Further analysis reveals that Ma-POSS obviously increased the molecular weight by grafting PMMA to be a star-shaped macromolecule. And the residual C=C of POSS–PMMA dramatically increased the photosensitivity. Moreover, the star-shaped POSS–PMMA acting as a plasticizer dramatically enhances the mechanical properties and so reduces the photoinduced volume shrinkage of PQ/PMMA. Finally, by the use of the POSS–PMMA/PQ in a collinear holography system, it appeared to be promising for a fast but low bit error rate in holographic information storage. The current study thence has not only successfully synthesized photopolymer materials with potential for highly sensitive holographic storage applications but also investigated the microphysical mechanism of the impact of Ma-POSS on the holographic properties of PQ/PMMA photopolymer and clarified the thermal- and photoreaction processes of the POSS–PMMA/PQ photopolymer.

Revealing protein reactions using transient grating method: Photo-induced heating, volume change, and diffusion change

The transient grating (TG) method, which is one of the photothermal techniques, can enable sensitive detection of thermal energy with high temporal resolution based on changes in the refractive index of a material. In addition to thermal energy, the TG method can also detect any changes that affect the refractive index, such as changes in the partial molar volume and in the absorption spectrum far from the probe wavelength. In this Perspective, recent studies on chemical reaction dynamics of proteins using the TG method are reviewed and discussed. To reveal the reaction schemes of proteins, it is particularly important to detect dynamics that cannot be detected by optical spectroscopy (spectrally silent dynamics), such as enthalpy changes, conformational changes, and changes in intermolecular interactions (protein–water, protein–protein, protein–lipids, and protein–DNA). The TG method is appropriate and powerful for such applications. Spectrally silent dynamics have clearly been observed by monitoring time-resolved diffusion and volume changes. Furthermore, the impact of the structural fluctuation of proteins on their reactivity has been successfully demonstrated by monitoring the thermal expansion and compressibility changes of short-lived intermediates. For expansion of the TG application to non-photochemical reactions, one attempt using the stopped flow-TG technique is described. Future possible applications of the TG method are suggested.

Formation of Ordered Nanostructures of Target Geometry Using Photo-Induced Volume Charge

Formation of Ordered Nanostructures of Target Geometry Using Photo-Induced Volume Charge

Miniaturized photogenerated electro-optic axicon lens Gaussian-to-Bessel beam conversion.

We experimentally demonstrate an electro-optic Gaussian-to-Bessel beam-converter miniaturized down to a 30×30 μm pixel in a potassium-lithium-tantalate-niobate (KLTN) paraelectric crystal. The converter is based on the electro-optic activation of a photoinduced and reconfigurable volume axicon lens achieved using a prewritten photorefractive funnel space-charge distribution. The transmitted light beam has a tunable depth of field that can be more than twice that of a conventional beam with the added feature of being self-healing.

The dynamics of photoinduced defect creation in amorphous chalcogenides: The origin of the stretched exponential function

The article discusses the dynamics of photoinduced defect creations (PDC) in amorphous chalcogenides, which is described by the stretched exponential function (SEF), while the well known photodarkening (PD) and photoinduced volume expansion (PVE) are governed only by the exponential function. It is shown that the exponential distribution of the thermal activation barrier produces the SEF in PDC, suggesting that thermal energy, as well as photon energy, is incorporated in PDC mechanisms. The differences in dynamics among three major photoinduced effects (PD, PVE, and PDC) in amorphous chalcogenides are now well understood.

Photoinduced Volume Transition in Liquid Crystalline Polymer Gels Swollen by a Nematic Solvent.

Nematic liquid crystalline (LC) cross-linked polymer gel sheets containing 3 mol % azobenzene (Az) unit were prepared and swollen by a nematic solvent of 4'-pentyl-4-cyanobiphenyl (5CB). This 5CB-swollen gel sheet exhibited a discontinuous volume change around the nematic-isotoropic phase transition temperature of the LC gel (TNIG). UV irradiation at a temperature slightly lower than TNIG provoked a large volume transition (expansion) due to a loss of nematic order within the gel sheet caused by the trans-to-cis photoisomerization of Az. The volume was reverted by irradiation with 436 nm light. By templating the colloidal crystal film of monodispersed silica particles, a LC gel sheet possessing a microporous structure was also prepared. Due to the facilitated diffusion of 5CB, the microporous LC gel exhibited significant enhancements in the extent and rate of the photoinduced volume transition.

Holographic studies of photoinduced anisotropy in molecular glassy films containing diphenylamine azochromophores

Photoinduced anisotropy (PA) is experimentally studied in three molecular glassy films synthesized in our Faculty and containing diphenylamine based azochromophores {4-((4-nitrophenyl)diazenyl)-N-(4-((4-nitrophenyl)diazenyl)phenyl)-N-(2-trityloxy)ethyl) benzeneamine (shortly K-D-24), 4-((2-chloro-4-tritylphenyl)diazenyl)-N-(4-((2-chloro-4-tritylphenyl)diazenyl)phenyl)-N-(2-(trityloxy)ethyl)benzenamine (shortly K-D-25), 4,4'-(2-(trityloxy)ethylazanediyl)bis(4,1-phenylene)bis(diazene-2,1-diyl)dibenzonitrile (shortly K-D-32) } and, for comparison, in an a-As2S3 film. Holographic method enabling simultaneous measurements of s- and p-polarized diffracted light powers was applied in both transmission and reflection modes. Holographic grating recording with the period of 2 μm was made by two equally strong 532 nm p- polarized laser beams with total light intensity of 0.81 W/cm2. The readout was made by 633 nm circularly polarized beam, and the s- and p-polarized components of diffracted light were separated by polarization beam splitter prism. PA was characterized by diffracted power difference (DPD), Ps − Pp, and by anisotropy contrast A = (ns − np)/(ns + np), ns and np being the diffraction efficiencies for s- and p-polarized light. DPD exhibited markedly different kinetic behaviour in transmission and reflection modes. There was a negative minimum in transmission mode in all samples, and a growth with oscillations up to saturation in reflection mode. Small initial DPD maxima were specific to a-As2S3 film. The highest PA was found in K-D-24 film in transmission mode (A=-0.23) and in K-D-25 film in reflection mode (A=0.49). Holographic recording efficiency and PA do not correlate. In our opinion, PA in transmission mode of molecular glasses is due to the photoinduced volume processes including trans-cis photoisomerization, chromophore orientation and mechanical stress modulation. In the case of a-As2S3 film these photoinduced volume processes include photoinduced structural changes, D-centre orientation and, again, mechanical stress modulation. All these processes lead to a photoinduced birefringence. Surface relief grating recording and polarization-dependent reflection are responsible for diffractive anisotropy in reflection mode.

Structural volume changes upon triplet formation of water-soluble porphyrins depend on the resonant effect of the substituents

Laser-induced optoacoustic spectroscopy was applied to evaluate the photoinduced structural volume changes upon triplet state formation, Δ(T)V, of an aqueous solution of 5,10,15,20-tetrakis-(4-carboxyphenyl)-porphin. Two molecular forms differing in the ionization state of the carboxylic groups at the para-position of the phenyl ring were studied. The contractions, Δ(T)V, for all water-soluble 5,10,15,20-tetra-aryl-porphyrin compounds studied to date show a linear correlation with the Hammett resonant σ(R) constant. This indicates that the resonance electronic communication spreading over the π-orbitals between the meso-aryl rings and the porphyrin macrocycle determines the molecular contraction of the aqueous sphere around the macrocycle in the triplet state.

Unlocking of interlocked heteropolymer gel by light: photoinduced volume phase transition in an ionic liquid from a metastable state to an equilibrium phase

An azobenzene-containing heteropolymer gel in an ionic liquid exhibits thermally reversible volume phase transition when the azobenzene moiety mainly exists in the cis-state, whereas the transition becomes irreversible when it is in the trans-state and an interlocked collapsed state is stabilized; however, the unlocking of the metastable state occurs by UV light irradiation.

Photoinduced Volume Changes of Obliquely and Flatly Deposited Amorphous AsSe Films Universal Description of the Kinetics

Recently, we have constructed structural models for flatly deposited amorphous Se (a-Se) and using these configurations we have developed atomic scale model of photoinduced volume changes in this type of films. In this paper the same work on obliquely deposited thin film is presented. Universal description for the kinetics of photoinduced volume change in chalcogenide glasses is proposed based on our results. Our model containing reversible (transient) and irreversible (metastable) parts for kinetics fits well the experimental results of both obliquely and flatly deposited a-AsSe thin films. Finally, we make a brief comment on stretched exponential function which could also provide a quite good fit to experimental data.

Photoinduced mass-transport based holographic recording of surface relief gratings in amorphous selenium films

Surface relief gratings formation in amorphous selenium thin films in two recording configurations with light intensity modulation were studied in situ by real-time atomic force microscopy and diffraction efficiency measurements. We report observation of mass transport effect in films induced by band-gap irradiation when the light polarization of the recording beams has a component along the light intensity gradient (“p-p” scheme of recording) that allows obtaining giant stable gratings in this versatile chalcogenide material. On the contrary, only a pure scalar weak grating caused by photoinduced volume shrinkage is obtained in the “s-s” recording configuration, even for long-term irradiation.

On photoinduced volume change in amorphous selenium: Quantum chemical calculation and Raman spectroscopy

Hartree–Fock ab initio Raman spectra calculations and Raman spectroscopic measurements were carried out on amorphous selenium in order to identify the characteristic vibrational mode due to sigma bonds. Variations in measured peak intensity were observed as a consequence of band gap light illumination. Based on our previous theoretical investigations we originate these intensity variations from photoinduced covalent bond breaking.

Photoinduced volume changes in obliquely deposited a‐Se

AbstractThe structures and the photoinduced volume changes of obliquely deposited amorphous selenium were studied using Molecular Dynamics computer simulation. Obliquely deposited a‐Se thin films contain larger voids than the flatly deposited ones. Our computer simulations confirmed that the preparation method strongly determines the photoinduced changes of the chalcogenide glasses. We described in detail for the first time the complex atomic rearrangements occurring on photo‐excitation in porous samples, which are reversible and irreversible photo contraction/expansion, bond breakings and formations (both inter‐ and intrachain). A model for the kinetics of the photoinduced volume changes of flatly and obliquely deposited chalcogenide thin films is presented. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamics of principal photoinduced effects in amorphous chalcogenides: In‐situ simultaneous measurements of photodarkening, volume changes, and defect creation

AbstractTo understand the direct relation among photodarkening (PD), photoinduced volume change (PVC), and photoinduced defect creation (PDC), we perform in‐situ simultaneous measurements of all three phenomena, i.e. optical absorption coefficient (for PD), surface height (for PVC), and photocurrent which monitors PDC, in amorphous As2Se3 films. The time evolution of PDC during light excitation is empirically described by a stretched exponential function: 1 ‐ exp[‐(t /τ)β], where τ is the effective response time and β (< 1.0) the dispersion parameter, while we have found that the PVC and PD were essentially given by a simple exponential function (β = 1). The value of τ for the PDC is very much smaller than those for the PVC and PD. As the time evolutions for all three phenomena are independent of each others, there may be no direct relationship among them. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoresponsive Nanogels Based on Photocontrollable Cross-Links

We present a new and general strategy for preparing photoresponsive nanogels. It is based on using light to reversibly change the cross-linking density of nanogel particles to control their swelling degree in aqueous solution. This control mechanism allows for gradual volume change of nanogel particles by light. For proof of concept, diblock copolymers composed of poly(ethylene oxide) and poly[2-(2-methoxyethoxy)ethyl methacrylate-co-4-methyl-[7-(methacryloyl)oxyethyloxy]coumarin] (PEO-b-P(MEOMA-co-CMA)) were synthesized; nanogels could easily be prepared by first photo-cross-linking the micellar aggregates at T > LCST of the P(MEOMA-co-CMA) block through dimerization of coumarin side groups upon absorption of λ > 310 nm UV light and then cooling the solution to T < LCST to obtain cross-linked water-soluble polymer nanoparticles. Under λ < 260 nm UV light, the reverse photocleavage of cyclobutane rings could be used to reduce the cross-linking density, leading to the swelling of nanogel particles with a volume increase by about 90%. The reversibility of the photoinduced volume change, the effects of the molecular weight of P(MEOMA-co-CMA) block and the content of coumarin groups on the photoresponsive behavior, and the use of nanogel particles for photocontrolled release were investigated.

Photoinduced ultrafast local volume changes in intermediate-valence solids

We present a theoretical model for the description of the ultrafast structural response of intermediate-valence solids to femtosecond laser excitation. The approach includes the calculation of the free energy of the hot electrons produced by the laser pulse and the determination of the changes in the thermodynamic and elastic properties of the solid as a consequence of the excitation. In particular and based on the promotional Ramirez-Falicov model, we consider the femtosecond laser heating of $\ensuremath{\alpha}$ cerium and the subsequent ultrafast lattice expansion dynamics. For this purpose, we determine the thermodynamic properties of cerium at very high electronic temperatures (simulating the laser excitation). The possibility for a nonequilibrium photoinduced inverse volume collapse transition is discussed. We consider both the laser-excited and the unexcited parts of the system in order to account for inertial confinement. The thermodynamic properties are obtained as function of time and used to calculate the shock velocity variation and the time scale for expansion of the heated spot into the surrounding (unheated) part of the sample. A transition on a subpicosecond time scale is predicted.

Structure and photoinduced volume changes of obliquely deposited amorphous selenium

Atomic scale computer simulations on structures and photoinduced volume changes of flatly and obliquely deposited amorphous selenium (a-Se) films have been carried out in order to understand how the properties of chalcogenide glasses are influenced by their preparation method. Obliquely deposited a-Se thin films contain more coordination defects and larger voids than the flatly deposited ones. To model the photoinduced volume changes the electron excitation and hole creation were treated independently within the framework of tight-binding formalism. Covalent and interchain bond breakings and formations were found. The obliquely deposited samples containing voids showed a wide spectrum of photoinduced structural changes in the microscopic level and volume changes in the macroscopic level.

To the kinetics of photoinduced volume changes in chalcogenide glasses

Recent experimental data on the dynamics of photoinduced volume changes in chalcogenide glasses are analyzed within a simple phenomenological model. Both kinetics of the volume expansion under continuous irradiation and that of the relaxation after the illumination is switched off are considered. Comparison between theoretical results and experimental data provides a quantitative estimate of the local conversion rate of structural units responsible for the effect into the expanded states. Furthermore, this comparison shows that the conversion rate in a-As2Se3 is several times smaller than that in a-Se.

Reversibly Photo-Responsive Polymer Surfaces for Controlled Wettability

Photochromic spiropyran molecules are utilized as additives for the development of polymer surfaces whose wetting characteristics can reversibly respond to irradiation with laser beams of properly chosen photon energy. The hydrophilicity is enhanced upon UV laser irradiation due to the photo-induced isomerization of the non-polar spiropyran molecules to the polar merocyanine. The situation is reversed upon green laser irradiation. Micropatterning of the photochromic-polymer films using soft lithography or photo-polymerization techniques affects their wettability towards a more hydrophobic or more hydrophilic behavior depending on the dimensions of the patterned features and on the hydrophilicity/hydrophobicity of the flat surface. The light-induced wettability variations of the structured surfaces are enhanced by up to a factor of three as compared to those on the flat surfaces. This enhancement is attributed to the photo-induced reversible volume changes to the imprinted gratings, which additionally contribute to the wettability changes due to the light-induced photochromic interconversions.

Microscopic and macroscopic models of photo-induced volume changes in amorphous selenium

We have proposed a new explanation for the photo-induced volume changes in chalcogenide glasses. We have found that the covalent bond breaking occurs in these glasses with excited electrons, whereas holes contribute to the formation of inter-chain bonds. We have calculated the charge distribution in a-Se, too.