Photoinduced Volume Changes Research Articles

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.

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.

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

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

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.

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.

In-situ real-time simultaneous measurements of photoinduced bandgap and volume changes in amorphous chalcogenide films

To understand the dynamics and correlations between photodarkening (PD) and photoinduced volume changes (PVC) in amorphous chalcogenides, a simultaneous PD and PVC measuring system based on computer analyzed spectroscope and phase-shifting interferometer (PSI) has been developed. This new system provides us the records of both PD and PVC in amorphous chalcogenides during illumination with common time axis. The time evolutions of PD and PVC are represented by a stretched exponential function and a just exponential function, respectively, suggesting that the dynamics of the PD is different from the PVC in a-As2Se3 films.

Photoinduced volume change in arsenic chalcogenides by band-gap light

Photoinduced structural changes in molecular semicrystalline ${\mathrm{As}}_{4}{\mathrm{Se}}_{3}$ films have been characterized by extended x-ray absorption fine structure and x-ray diffraction under in situ band-gap laser illumination. Transient and permanent changes in the local and long-range structure have been determined quantitatively. In contrast to fully amorphous arsenic selenide films, a photoinduced contraction has been observed in semicrystalline ${\mathrm{As}}_{4}{\mathrm{Se}}_{3}$ films. A comprehensive phenomenological model is proposed for the photoinduced volume change in As-based chalcogenides. This model is based on two competing processes viz. intermolecular interaction through Coulombic repulsive force that results in photoexpansion, and cross-linking of molecular units through bond switching that causes photocontraction. A guideline is presented for selecting chalcogenide glass composition with specific photoinduced volume change characteristics.

In situ simultaneous measurements of photodarkening and photoinduced volume changes in chalcogenide glasses

To understand the dynamics and correlations between photodarkening (PD) and photoinduced volume changes (PVC) in chalcogenide glasses, we built up an in situ simultaneous PD and PVC measuring system based on a computer controlled spectroscope and a phase-shifting interferometer (PSI). This new system provides us the records of both PD and PVC in chalcogenide glasses during illumination with a common time axis. We have observed that the PVC reaches equilibrium faster than the PD in a-As2Se3 films.

Universal feature of photo-induced volume changes in chalcogenide glasses

We have investigated in chalcogenide glasses the microscopic processes caused by illumination using tight-binding molecular dynamics computer simulation. After photon absorption we treated the excited electron and hole independently. We found covalent bond breaking in amorphous networks with photo-induced excited electrons, whereas excited holes contribute to the formation of inter-chain bonds. We also observed a correlated macroscopic volume change of the amorphous sample. Our results provide a new and universal description, which can explain simultaneously the photo-induced volume expansion and shrinkage. This model is supported by the results of recent measurements.

Combination of microstructuring and laser-light irradiation for the reversible wettability of photosensitised polymer surfaces

The wetting characteristics of surfaces of polymers doped with photochromic spiropyran molecules can be tuned when irradiated with laser beams of properly chosen photon energy. In particular, UV laser pulses at 308 nm are responsible for the enhancement of the hydrophilicity of the surfaces, since the embedded non-polar spiropyran molecules convert to their polar merocyanine isomers upon UV absorption. The process is reversed upon irradiation with green laser pulses at 532 nm. When the photochromic-polymeric surfaces are micropatterned using soft lithography or photo-polymerisation techniques, they can change their wettability towards a more hydrophobic or more hydrophilic behaviour depending on the dimensions of the patterned features and on the hydrophilicity-hydrophobicity of the flat surface. Furthermore, the light-induced wettability variations on these structured surfaces are greatly enhanced compared to the flat surfaces. This significant increase to the wettability changes is attributed to the combination of the photochromic interconversions upon laser irradiation together with the photoinduced reversible volume changes of the patterned features.

Photocontrolled Variations in the Wetting Capability of Photochromic Polymers Enhanced by Surface Nanostructuring

The wetting characteristics of surfaces of polymers doped with photochromic spiropyran molecules can be tuned when irradiated with laser beams of properly chosen photon energy. The hydrophilicity is enhanced upon UV laser irradiation since the embedded nonpolar spiropyran molecules convert to their polar merocyanine isomers. The process is reversed upon green laser irradiation. Structuring of the photochromic polymeric surfaces with soft lithography enhances significantly the hydrophobicity of the system, indicating that the water droplets on the patterned features interact with air that is trapped in the microcavities, thus creating superhydrophobic air-water contact areas. Furthermore, the light-induced wettability variations of the structured surfaces are enhanced by a factor of 3 compared to those on the flat surfaces. This significant enhancement is attributed to the photoinduced reversible volume changes to the imprinted gratings, which additionally contribute to the wettability changes due to the light-induced photochromic interconversions.

Photoinduced Volume Changes in Amorphous Selenium

We have modeled the photoinduced volume change in amorphous selenium. After photon absorption, we treated the excited electron and hole independently within the framework of the tight-binding formalism. We found covalent bond breaking in amorphous networks with photoinduced excited electrons, whereas excited holes contribute to the formation of interchain bonds. We also observed a correlated volume change of the amorphous samples. Our results provide a new and universal description, which can simultaneously explain the photoinduced volume expansion and shrinkage. This model is supported by very recent in situ surface height measurements for amorphous selenium.

Holographic recording in [Sb(PO3)3]n–Sb2O3 glassy films by photoinduced volume and refraction index changes

Glassy films of 0.2[Sb(PO3)3]n–0.8Sb2O3 with 0.8μm-thickness were deposited on quartz substrates by electron beam evaporation. A contraction in the film thickness (photoinduced decrease in volume) and photobleaching effect associated with a decrease of up to 25% in the index of refraction has been observed in the films after irradiation near the bandgap (3.89eV), using the 350.7nm (3.54eV) Kr+ ion laser line with 2.5W/cm2 for 30min. A loss of 30% in the phosphorus concentration was measured by wavelength dispersive X-ray microanalysis in the film after laser irradiation with 5.0W/cm2 for 1.0h. These photoinduced changes in the samples are dependent on the power density and intensity profile of the laser beam. Using a Lloyd’s mirror setup for continuous wave holography it was possible to record holographic gratings with period from 500nm up to 20μm and depth profile of ∼50nm in the films after laser irradiation with 5.0W/cm2 for 1h. Real-time diffraction efficiency measurements have shown that ultraviolet irradiation induces first a refractive index grating formation, and after this, the photocontraction effect takes place generating an irreversible relief grating. Diffraction efficiency up to 10% was achieved for the recorded gratings. 3D-refraction index measurements and atomic force microscopy images are presented.