Sofia Trakhtenberg

Methylene blue adsorption on thymine based polyvinylphenylsulfonate films

The immobilization of thymine‐containing copolymers of vinylphenylsulfonate (VPS) and vinylbenzylthymine (VBT) on a nonreactive substrate has been investigated. These polymers are environmentally benign, water‐soluble and when irradiated with low levels of UV light undergo a 2π+2π photodimerization reaction of the thymine moieties. These photoinduced dimers form a crosslinked network that renders the polymer significantly less soluble in water. Consequently the irradiated polymer is immobilized on the substrate, allowing removal of unexposed regions by simple aqueous wash. Visualization of the photoresist is done by “toning” the remaining anionic copolymer with the cationic dye methylene blue. By evaluating the color density of the crosslinked, toned films by UV‐Vis spectroscopy, this report describes the impact of copolymer composition and curing conditions on polymer photoreactivity. Mechanistic rationale is proposed.

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.

Influence of pH and Salt on the Photocrosslinking in Polyelectrolyte Thymine‐Containing Films

Photocrosslinking of thymine‐based water‐soluble polymer films was investigated at varying preparation conditions. Adding salt or decreasing the pH of the solution from which the films were cast resulted in the decreased efficiency of photoimmobilization, while increasing the pH was found to increase the photoimmobilization efficiency. A mechanistic rationale for the observed effects is proposed.

Chapter 13 Non-Catalytic Photo-Induced Immobilization Processes in Polymer Films

This chapter describes non-catalytic photo-induced immobilization processes in polymer films. These processes are fundamental to a variety of applications such as microelectronics, imaging, and release mechanisms. The main focus of this chapter is on photopolymers containing thymine, a DNA base. In the first section, the historical account of applications of photoresist polymers is presented, and the processes of thymine photodimerization and its reversal are introduced. The second section discusses the mechanism of ultraviolet (UV) light-induced photodimerization of thymine. Concerted reaction resulting in the formation of cyclobutane rings is discussed in the context of Woodward–Hoffmann Frontier Molecular Orbital theory. The third section deals with synthetic polymers that incorporate thymine moieties as pendant groups. In this section examples are given of both organic- and water-soluble photopolymers, which can be immobilized by photo-induced crosslinking, and the applications of those polymers. The fourth section focuses on soluble polymers that are immobilized as result of exposure to irradiation, such as UV light. The kinetics of immobilization is described in the context of Florys theory of network formation. The fifth section describes various methods known to trigger the reverse crosslinking process, resulting in the re-solubilization of photo-immobilized films. The sixth section presents some thoughts on possible future directions and potential opportunities for this technology.

The Effects of Irradiation Dose and of Photopolymer Composition on the Dissolution of Entrapped Dyes

Dissolution kinetics of dyes entrapped in photocrosslinked polymer matrix were investigated. Films containing thymine‐based bioinspired photopolymers and non‐toxic dyes were deposited on the polyethylterephthalate (PET) substrate from aqueous solutions. The films were cured by exposure to various UV‐irradiation doses (λ=254 nm) and developed in a weakly acidic aqueous medium. The UV‐Vis spectra of the films before and after curing and development were taken and the intensities of the bands corresponding to the absorbance of the respective dyes entrapped in the films were monitored for a variety of irradiation doses, development times, polymer compositions and two different dyes.