Sensitizer Molecules Research Articles

Perylene Sensitization of Fullerenes for Improved Performance in Organic Photovoltaics

AbstractWe present the addition of an energy relay dye to fullerenes resulting in increased light harvesting and significantly improved power conversion efficiency for organic photovoltaic (OPV) devices. Although exhibiting excellent properties as electron acceptors, visible light absorption of fullerenes is limited. Strongly light absorbing donor materials are needed for efficient light harvesting in the thin active layer of OPV devices. Therefore, photocurrent generation and thus power conversion efficiency of this type of solar cell is confined by the overlap of the relatively narrow absorption band of commonly used donor molecules with the solar spectrum. Herein the concept of fullerene dye sensitization is presented, which allows increased light harvesting on the electron acceptor side of the heterojunction. The concept is exemplarily shown for an UV absorbing small molecule and a near infrared absorbing polymer, namely hexa‐peri‐hexabenzocoronene (HBC) and Poly[2,1,3‐benzothiadiazole‐4,7‐diyl[4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b']dithiophene‐2,6‐diyl]] (PCPDTBT), respectively. In both systems remarkably higher power conversion efficiency is achieved via perylene sensitization of the fullerene acceptor. Steady state photoluminescence, transient absorption and transient photocurrent decay studies reveal pathways of the additionally generated excited states at the sensitizer molecule. The findings suggest fluorescence resonance energy transfer from the photo‐excited dye to the fullerene enabling decoupling of light absorption and charge transport. The presented sensitization method is proposed as a viable new concept for performance enhancement in organic photovoltaic devices.

Solution-processed bulk heterojunction organic solar cells with high polarity small molecule sensitizer

A new sensitizer molecule, HMBI (9,18-(di-2-hexyldecyl)-2,11-dimethoxy-9,18-dihydrobenzo[5,6]-s-indaceno[1,2-b]indeno[2,1-h]carbazol-6,15-dione), containing electron-donating carbazole and electron-accepting diketone units, has been synthesized for solution-processed bulk heterojunction organic solar cells. The HMBI material has good solubility in common organic solvents. Its HOMO and LUMO energy levels were found to be at 5.6 and 3.0 eV, respectively. It has absorption bands ranging from 300 to 500 nm. Dispersion of HMBI molecules in the P3HT/PCBM blend broadens the absorption bands over the spectral range of 350–500 nm. Uniform thin film devices doped with varying concentration of HMBI, incorporated within the P3HT/PCBM blend, were fabricated. The 3 wt% of HMBI doping produces an improvement in power-conversion efficiency (PCE) up to 11.5% compared with the reference P3HT/PCBM device. Efficient light harvesting caused by HMBI sensitizer molecules primarily yields increased carrier generation and short-circuit current. In addition, some morphological improvements in the P3HT/PCBM system may contribute to the generation of enhanced photocurrent.

Photosensitizer drug delivery via an optical fiber.

An optical fiber has been developed with a maneuverable mini-probe tip that sparges O(2) gas and photodetaches pheophorbide (sensitizer) molecules. Singlet oxygen is produced at the probe tip surface which reacts with an alkene spacer group releasing sensitizer upon fragmentation of a dioxetane intermediate. Optimal sensitizer photorelease occurred when the probe tip was loaded with 60 nmol sensitizer, where crowding of the pheophorbide molecules and self-quenching were kept to a minimum. The fiber optic tip delivered pheophorbide molecules and singlet oxygen to discrete locations. The 60 nmol sensitizer was delivered into petrolatum; however, sensitizer release was less efficient in toluene-d(8) (3.6 nmol) where most had remained adsorbed on the probe tip, even after the covalent alkene spacer bond had been broken. The results open the door to a new area of fiber optic-guided sensitizer delivery for the potential photodynamic therapy of hypoxic structures requiring cytotoxic control.

Abstract 3234: Fiber optic-guided photosensitizer drug delivery

Abstract A fiber optic device has been developed with a maneuverable probe tip that sparges oxygen gas and photo-detaches pheophorbide (sensitizer) molecules. Singlet oxygen is produced at the probe tip surface which reacts with an alkene bridge causing the release of sensitizer upon fragmentation of a dioxetane intermediate. For optimal sensitizer release the probe tip was loaded with 0.3% sensitizer resulting, where crowding of pheophorbide molecules and self-quenching were kept to a minimum. The fiber optic device delivers pheophorbide molecules and singlet oxygen to discrete locations. Site-selective release of pheophorbide occurred in lipophilic media, it was quantitative in petrolatum (petroleum jelly, 100%), and was inefficient in toluene (5%) and water (<1%) due to poor the solvation. The results open the door to applications in tumor eradication in lipophilic and hypoxic structures requiring cytotoxic control. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3234. doi:10.1158/1538-7445.AM2011-3234

Entropically Driven Photochemical Upconversion

Conventional photochemical upconversion (UC) through homo-geneous triplet-triplet annihilation (TTA) is subject to several enthalpic losses that limit the UC margin. Here, we address one of these losses: the triplet energy transfer (TET) from the sensitizer to the emitter molecules. Usually, the triplet energy level of the emitter is set below that of the sensitizer. In our system, the triplet energy level of the emitter exceeds that of the sensitizer by ∼600 cm(-1). Choosing suitable concentrations for the sensitizer and emitter molecules, we can exploit entropy as a driving force for the migration of triplet excitation from the sensitizer to the emitter manifolds. Thereby we obtain a new record for the peak-to-peak TTA-UC energy margin of 0.94 eV. A modified Stern-Volmer analysis yields a TET rate constant of 2.0 × 10(7) M(-1) s(-1). Despite being relatively inefficient, the upconverted fluorescence is easily visible to the naked eye with irradiation intensities as low as 2 W cm(-2).

Numerical Simulations for the Efficiency Improvement of Hybrid Dye-microcrystalline Silicon pin-solar cells

ABSTRACTIn hybrid solar cells consisting of dye sensitizers incorporated in the i-layer of a microcrystalline silicon (μc-Si:H) pin solar cell the dye sensitizer molecules are embedded in the matrix and enhance the overall absorption of the dye-matrix system due to their high absorption coefficient in the spectral range interesting for photovoltaic applications. This contribution investigates the efficiency improvement of hybrid dye-μc-Si:H solar cells compared to pure μc-Si:H solar cells by simulation. The results indicate that, under optimum conditions, the efficiency can be improved by more than a factor of 1.2 compared to a pure μc-Si:H cell. The thickness reduction for the hybrid system can be as large as 50 % for the same efficiency. However, the efficiency improvement also depends on the amount of additionally induced defects in the matrix by the embedded dye molecules. Therefore, the simulations investigate the performance of the hybrid solar cell for different absorption enhancements and defect densities.

Metformin Decreases GnRH- and Activin-Induced Gonadotropin Secretion in Rat Pituitary Cells: Potential Involvement of Adenosine 5' Monophosphate-Activated Protein Kinase (PRKA)

Metformin is an insulin sensitizer molecule used for the treatment of infertility in women with polycystic ovary syndrome and insulin resistance. It modulates the reproductive axis, affecting the release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). However, metformin's mechanism of action in pituitary gonadotropin-secreting cells remains unclear. Adenosine 5' monophosphate-activated protein kinase (PRKA) is involved in metformin action in various cell types. Here, we investigated the effects of metformin on gonadotropin secretion in response to activin and GnRH in primary rat pituitary cells (PRP), and studied PRKA in rat pituitary. In PRP, metformin (10 mM) reduced LH and follicle-stimulating hormone (FSH) secretion induced by GnRH (10(-8) M, 3 h), FSH secretion, and mRNA FSHbeta subunit expression induced by activin (10(-8) M, 12 or 24 h). The different subunits of PRKA are expressed in pituitary. In particular, PRKAA1 is detected mainly in gonadotrophs and thyrotrophs, is less abundant in lactotrophs and somatotrophs, and is undetectable in corticotrophs. In PRP, metformin increased phosphorylation of both PRKA and acetyl-CoA carboxylase. Metformin decreased activin-induced SMAD2 phosphorylation and GnRH-induced mitogen-activated protein kinase (MAPK) 3/1 (ERK1/2) phosphorylation. The PRKA inhibitor compound C abolished the effects of metformin on gonadotropin release induced by GnRH and on FSH secretion and Fshb mRNA induced by activin. The adenovirus-mediated production of dominant negative PRKA abolished the effects of metformin on the FSHbeta subunit mRNA and SMAD2 phosphorylation induced by activin and on the MAPK3/1 phosphorylation induced by GnRH. Thus, in rat pituitary cells, metformin decreases gonadotropin secretion and MAPK3/1 phosphorylation induced by GnRH and FSH release, FSHbeta subunit expression, and SMAD2 phosphorylation induced by activin through PRKA activation.

Effect of Different Anchoring Groups on the Adsorption of Photoactive Compounds on the Anatase (101) Surface

The effect of replacing the anchoring carboxylate groups in the Ru(H(2)dcbpy)(2)(NCS)(2) (H(2)dcbpy = 4,4'-dicarboxylic acid-2,2'- bipyridine) photoactive dye was studied by computational density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The main emphasis in the study was to compare a series of attaching groups, including COOH, B(OH)(2), PO(OH)(2), SO(2)(OH), OH, NO(2), and SiCl(3), by the relative adsorption strength and geometry of the sensitizer molecules on the anatase (101) surface. Additionally, the substituent effect on the absorption signals in simulated UV-vis spectra was calculated with isolated dye molecules. Most of the selected substituents produced only small changes in the absorption characteristics of the dyes. However, OH groups were found to show a quite large blue-shift compared to traditional COOH anchor groups in the simulated UV-vis spectra, while NO(2) groups had an opposite effect of red-shifting the signals. On the other hand, although the NO(2) substituents on the bipyridine ligands led to favorable absorption characteristics, the calculated adsorption strength of the NO(2)-substituted bipyridine models on the surface of anatase (101) was much smaller than that of the COOH-substituted one, indicating that larger modifications are necessary for both attaching the dye molecules on the surface and for tuning the absorption properties of photoactive compounds in the DSSC applications. The computational methods utilized here proved to be an efficient tool to study the effect of subtle structural changes on the properties of the dye molecules.

The emergence and evolution of life in a "fatty acid world" based on quantum mechanics.

Quantum mechanical based electron correlation interactions among molecules are the source of the weak hydrogen and Van der Waals bonds that are critical to the self-assembly of artificial fatty acid micelles. Life on Earth or elsewhere could have emerged in the form of self-reproducing photoactive fatty acid micelles, which gradually evolved into nucleotide-containing micelles due to the enhanced ability of nucleotide-coupled sensitizer molecules to absorb visible light. Comparison of the calculated absorption spectra of micelles with and without nucleotides confirmed this idea and supports the idea of the emergence and evolution of nucleotides in minimal cells of a so-called Fatty Acid World. Furthermore, the nucleotide-caused wavelength shift and broadening of the absorption pattern potentially gives these molecules an additional valuable role, other than a purely genetic one in the early stages of the development of life. From the information theory point of view, the nucleotide sequences in such micelles carry positional information providing better electron transport along the nucleotide-sensitizer chain and, in addition, providing complimentary copies of that information for the next generation. Nucleotide sequences, which in the first period of evolution of fatty acid molecules were useful just for better absorbance of the light in the longer wavelength region, later in the PNA or RNA World, took on the role of genetic information storage.

Non-monotonic changes in clonogenic cell survival induced by disulphonated aluminum phthalocyanine photodynamic treatment in a human glioma cell line

BackgroundPhotodynamic therapy (PDT) involves excitation of sensitizer molecules by visible light in the presence of molecular oxygen, thereby generating reactive oxygen species (ROS) through electron/energy transfer processes. The ROS, thus produced can cause damage to both the structure and the function of the cellular constituents resulting in cell death. Our preliminary investigations of dose-response relationships in a human glioma cell line (BMG-1) showed that disulphonated aluminum phthalocyanine (AlPcS2) photodynamically induced loss of cell survival in a concentration dependent manner up to 1 μM, further increases in AlPcS2concentration (>1 μM) were, however, observed to decrease the photodynamic toxicity. Considering the fact that for most photosensitizers only monotonic dose-response (survival) relationships have been reported, this result was unexpected. The present studies were, therefore, undertaken to further investigate the concentration dependent photodynamic effects of AlPcS2.MethodsConcentration-dependent cellular uptake, sub-cellular localization, proliferation and photodynamic effects of AlPcS2 were investigated in BMG-1 cells by absorbance and fluorescence measurements, image analysis, cell counting and colony forming assays, flow cytometry and micronuclei formation respectively.ResultsThe cellular uptake as a function of extra-cellular AlPcS2 concentrations was observed to be biphasic. AlPcS2 was distributed throughout the cytoplasm with intense fluorescence in the perinuclear regions at a concentration of 1 μM, while a weak diffuse fluorescence was observed at higher concentrations. A concentration-dependent decrease in cell proliferation with accumulation of cells in G2+M phase was observed after PDT. The response of clonogenic survival after AlPcS2-PDT was non-monotonic with respect to AlPcS2 concentration.ConclusionsBased on the results we conclude that concentration-dependent changes in physico-chemical properties of sensitizer such as aggregation may influence intracellular transport and localization of photosensitizer. Consequent modifications in the photodynamic induction of lesions and their repair leading to different modes of cell death may contribute to the observed non-linear effects.

Sensitization of Nanocrystalline TiO2 Anchored with Pendant Catechol Functionality Using a New Tetracyanato Ruthenium(II) Polypyridyl Complex

We have synthesized a new photoactive ruthenium(II) complex having a pendant catechol functionality (K(2)[Ru(CN)(4)(L)] (1) (L is 4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol) for studying the dynamics of the interfacial electron transfer between nanoparticulate TiO(2) and the photoexcited states of this Ru(II) complex using femtosecond transient absorption spectroscopy. Steady-state absorption and emission studies revealed that the complex 1 showed a strong solvatochromic behavior in solvents or solvent mixtures of varying polarity. Our steady-state absorption studies further revealed that 1 is bound to TiO(2) surfaces through the catechol functionality, though 1 has two different types of functionalities (catecholate and cyanato) for binding to TiO(2) surfaces. The longer wavelength absorption band tail for 1, bound to TiO(2) through the proposed catecholate functionality, could also be explained on the basis of the DFT calculations. Dynamics of the interfacial electron transfer between 1 and TiO(2) nanoparticles was investigated by studying kinetics at various wavelengths in the visible and near-infrared region. Electron injection to the conduction band of the nanoparticulate TiO(2) was confirmed by detection of the conduction band electron in TiO(2) ([e(-)](TiO(2))(CB)) and cation radical of the adsorbed dye (1(*+)) in real time as monitored by transient absorption spectroscopy. A single exponential and pulse-width limited (<100 fs) electron injection was observed. Back electron transfer dynamics was determined by monitoring the decay kinetics of 1(*+) and [e(-)](TiO(2))(CB). This is the first report on ultrafast ET dynamics on TiO(2) nanoparticle surface using a solvatochromic sensitizer molecule.

Photosensitized oxidation of alkenes with dendrimers as microreactors: controllable selectivity between energy and electron transfer pathway

Carboxylic acid terminated poly(aryl ether) dendrimers were used as microreactors to conduct the photooxidation of trans-stilbene and trans,trans-1,4-diphenyl-1,3-butadiene (DPB) sensitized by 9,10-dicyanoanthracene (DCA) in aqueous media. The photooxidation pathways can be successfully controlled by encapsulating the substrate and sensitizer molecules in the same or different sets of dendrimers. The singlet oxygen can transfer from one dendrimer to another. After the photoreaction, products could be more easily extracted from a dendrimer than from a micelle or a vesicle, and the dendrimer can be simply recovered by neutralization of the solution and reused.

Quantum Conversion Management of the Sensitized Semiconductor Electrodes: Strategies against Energy Dissipation

Strategies and experimental methods in photoelectrochemistry for the enhancement of light harvest performance and quantum conversion efficiency at the photo-sensitized semiconductor electrode are reviewed. Highlighted particularly in this review are the material solutions to the suppression of energy dissipation at sensitizer molecules and the semiconductor surface. Discussions are focused on sensitization of a thin n-type semiconductor, typically TiO2, with organic dyes and inorganic nanocrystals (quantum dots) that have high extinction coefficients. Based on the strategies proposed, current developments by our group of low-cost dye-sensitized solar cells by means of printable materials and technologies are also introduced.

On the efficiency limit of triplet–triplet annihilation for photochemical upconversion

Photochemical upconversion is performed, whereby emitter triplet states are produced through triplet energy transfer from sensitizer molecules excited with low energy photons. The triplet emitter molecules undergo triplet-triplet annihilation to yield excited singlet states which emit upconverted fluorescence. Experiments comparing the 560 nm prompt fluorescence when rubrene emitter molecules are excited directly, using 525 nm laser pulses, to the delayed, upconverted fluorescence when the porphyrin sensitizer molecules are excited with 670 nm laser pulses reveal annihilation efficiencies to produce excited singlet emitters in excess of 20%. Conservative measurements reveal a 25% annihilation efficiency, while a direct comparison between the prompt and delayed fluorescence yield suggests a value as high as 33%. Due to fluorescence quenching, the photon upconversion efficiencies are lower, at 16%.

The Effect of Heavy Atoms on Photoinduced Electron Injection from Nonthermalized and Thermalized Donor States of MII–Polypyridyl (M=Ru/Os) Complexes to Nanoparticulate TiO2 Surfaces: An Ultrafast Time‐Resolved Absorption Study

We have synthesized ruthenium(II)- and osmium(II)-polypyridyl complexes ([M(bpy)(2)L](2+), in which M=Os(II) or Ru(II), bpy=2,2'-bipyridyl, and L=4-(2,2'-bipyridinyl-4-yl)benzene-1,2-diol) and studied the interfacial electron-transfer process on a TiO(2) nanoparticle surface using femtosecond transient-absorption spectroscopy. Ruthenium(II)- and osmium(II)-based dyes have a similar molecular structure; nevertheless, we have observed quite different interfacial electron-transfer dynamics (both forward and backward). In the case of the Ru(II)/TiO(2) system, single-exponential electron injection takes place from photoexcited nonthermalized metal-to-ligand charge transfer (MLCT) states. However, in the case of the Os(II)/TiO(2) system, electron injection takes place biexponentially from both nonthermalized and thermalized MLCT states (mainly (3)MLCT states). Larger spin-orbit coupling for the heavier transition-metal osmium, relative to that of ruthenium, accounts for the more efficient population of the (3)MLCT states in the Os(II)-based dye during the electron-injection process that yields biexponential dynamics. Our results tend to suggest that appropriately designed Os(II)-polypyridyl dye can be a better sensitizer molecule relative to its Ru(II) analogue not only due to much broader absorption in the visible region of the solar-emission spectrum, but also on account of slower charge recombination.

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

Researchers are intensively investigating photochemical water splitting as a means of converting solar to chemical energy in the form of fuels. Hydrogen is a key solar fuel because it can be used directly in combustion engines or fuel cells, or combined catalytically with CO(2) to make carbon containing fuels. Different approaches to solar water splitting include semiconductor particles as photocatalysts and photoelectrodes, molecular donor-acceptor systems linked to catalysts for hydrogen and oxygen evolution, and photovoltaic cells coupled directly or indirectly to electrocatalysts. Despite several decades of research, solar hydrogen generation is efficient only in systems that use expensive photovoltaic cells to power water electrolysis. Direct photocatalytic water splitting is a challenging problem because the reaction is thermodynamically uphill. Light absorption results in the formation of energetic charge-separated states in both molecular donor-acceptor systems and semiconductor particles. Unfortunately, energetically favorable charge recombination reactions tend to be much faster than the slow multielectron processes of water oxidation and reduction. Consequently, visible light water splitting has only recently been achieved in semiconductor-based photocatalytic systems and remains an inefficient process. This Account describes our approach to two problems in solar water splitting: the organization of molecules into assemblies that promote long-lived charge separation, and catalysis of the electrolysis reactions, in particular the four-electron oxidation of water. The building blocks of our artificial photosynthetic systems are wide band gap semiconductor particles, photosensitizer and electron relay molecules, and nanoparticle catalysts. We intercalate layered metal oxide semiconductors with metal nanoparticles. These intercalation compounds, when sensitized with [Ru(bpy)(3)](2+) derivatives, catalyze the photoproduction of hydrogen from sacrificial electron donors (EDTA(2-)) or non-sacrificial donors (I(-)). Through exfoliation of layered metal oxide semiconductors, we construct multilayer electron donor-acceptor thin films or sensitized colloids in which individual nanosheets mediate light-driven electron transfer reactions. When sensitizer molecules are "wired" to IrO(2).nH(2)O nanoparticles, a dye-sensitized TiO(2) electrode becomes the photoanode of a water-splitting photoelectrochemical cell. Although this system is an interesting proof-of-concept, the performance of these cells is still poor (approximately 1% quantum yield) and the dye photodegrades rapidly. We can understand the quantum efficiency and degradation in terms of competing kinetic pathways for water oxidation, back electron transfer, and decomposition of the oxidized dye molecules. Laser flash photolysis experiments allow us to measure these competing rates and, in principle, to improve the performance of the cell by changing the architecture of the electron transfer chain.

Acceleration of guanine oxidation under visible light irradiation by photon upconversion based on triplet-triplet annihilation

We report the fluorescent polymer complex which can show fluorescence emission at 380 nm with the excitation of 520 nm in aqueous media. This photon upconversion based on triplet-triplet annihilation can efficiently take place via inter-molecular energy transfers between the Ru complex as a sensitizer and anthracene molecules as an emitter captured into the water-soluble network polymers. We performed the oxidation reaction of 2'-deoxyguanosine by riboflavin in the presence of the polymer complex with the visible light irradiation. It was clearly indicated that oxidative decomposition can be accelerated by UV light generation via upconversion based on triplet-triplet annihilation.

The local and observed photochemical reaction rates revisited

In a broad sense, photochemical reactions proceed through pathways involving several reaction steps. The initiation step is the absorption of energy both by the reactant or sensitizer molecules and in some cases, by the catalyst, leading to intermediate products that ultimately give rise to stable end products. Preferably, the reaction rate expression is derived from a proposed mechanism together with sound simplifying assumptions; otherwise, it may be adopted on an empirical basis. Under a kinetic control regime, the rate expression thus obtained depends on the local rate of photon absorption according to a power law whose exponent very often ranges from one half to unity. The kinetic expression should be valid at every point of the reactor volume. However, due to radiation attenuation in an absorbing and/or scattering medium, the value of the photon absorption rate is always a function of the spatial position. Therefore, the overall photochemical reaction rate will not be uniform throughout the entire reaction zone, and the distinction between local and volume average photochemical reaction rates becomes mandatory. Experimental values of reaction rates obtained from concentration measurements performed in well-mixed reaction cells are, necessarily, average values. Consequently, for validation purposes, experimental results from these cells must be compared with volume averages of the mechanistically or empirically derived local reaction rate expressions. In this work it is shown that unless the rate is first order with respect to the photon absorption rate or the attenuation in the absorbing and/or scattering medium is kept very low, when the averaging operation is not performed, significant errors may be expected.

Sensitization of TiO 2 nanoparticles in micro-emulsion by photo-excited dye molecules: A femtosecond transient absorption study

Photo-induced electron transfer reaction in controlled sized TiO 2 particles sensitized by catechol and quinizarin 6-sulfonate (Qz-6S) has been investigated using femtosecond transient absorption spectroscopy. Size-controlled TiO 2 nanoparticles were synthesized in reverse micelles using di-octyl sulfosuccinate (Aerosol-OT, AOT) as the surfactant stabilizer. The particle sizes of the nanoparticles were controlled by varying the water-to-surfactant molar ratio, w 0 = [H 2O]/[AOT]. Optical absorption measurements confirm that only strong coupling between the nanoparticles and the sensitizers can ensure sensitization the nanoparticles in the micro-emulsion media. Electron transfer process has been determined by monitoring electron in the conduction band in nanoparticle at 900 nm and parent cation in the visible region of the sensitizer molecules. Electron injection has been measured from the appearance signal of injected electron at 900 nm and it is found to be pulse-width (<50 fs) in both the systems. We have also carried out electron transfer studies of both the dye-nanoparticle systems in aqueous solutions where the particles have been prepared by sol–gel process and compared the data studied in micro-emulsion to see the effect of micro-environment.

Photosensitization of Bioinspired Thymine-Containing Polymers

Here, we report a sensitization study on a family of water-soluble photopolymers based on thymine. The goal of this study was to determine whether the presence of sensitizer molecules would promote photocrosslinking/immobilization of the polymers using low-energy irradiation (520 nm) as compared to the UV irradiation (approximately 280 nm) necessary for the standard photoinduced process to take place. With the aid of Eosin Y Spirit Soluble (EY) as a sensitizer, water-soluble polystyrene copolymers of vinylbenzylthymine-vinylbenzyltriethylammonium chloride (VBT-VBA) were immobilized after exposure to visible irradiation. By exciting the sensitizer molecule in the presence of VBT copolymers at a wavelength where absorption by the latter does not occur, the triplet state of the sensitizer is generated in high yields, and consequently, polymer photocross-linking takes place. UV-vis spectroscopy has been used to study the effect of irradiation dose, copolymer composition, and sensitizer concentration on the photoreactivity of VBT polymers. These studies demonstrate the feasibility of using Eosin Y as a sensitizer to achieve the thymine photodimer formation, resulting in immobilization of VBT-VBA-EY films on PET substrate. This provides complementary information on photoinduced immobilization of VBT-VBA films that are crucial for developing new classes of environmentally benign materials and new energy-saving methods.