Jerzy Paczkowski

Photophysical properties of rose bengal and its derivatives (XII)

We describe herein a series of new derivatives of tetrachloro tetraiodo (rose bengal) and report their emission and absorption characteristics. Photochemists and photobiologists may find several of these derivatives useful as alternative sources of singlet oxygen.

Development of new dyeing photoinitiators for free radical polymerization based on 3-methyl-1-phenyl-1H-pentaazacyclopenta[b]naphthalene skeleton III

Abstract Two dyes containing pyrazoloquinoxaline moiety have been synthesized and evaluated as the novel photoinitiators for free radical polymerization induced with the argon-ion laser. The kinetic study of photoinitiated polymerization, performed for viscous monomeric formulation with the use of the most effective dye, N -phenylglycine derivatives photoinitiating photoredox pairs, has shown an unusual kinetic property. The experimental data show the presence of the ‘Marcus inverted region’ like kinetic behavior. The analysis of the possible reasons of this specific feature suggested two possible processes that might be responsible for such a specific property. The first is the back electron transfer process and the second is the rate of the proton transfer that follows the photoinduced electron transfer (PET) process. In the paper, it is also shown that the structure of the dye has a strong effect on its polymerization photoinitiation ability. The dyes tested were prepared in a way that allows the coplanarization of the molecule skeleton and this causes an increase of the quantum yield of the triplet state formation.

Factors influencing the quantum yields for rose bengal formation of singlet oxygen

Abstract The φ for 1O2 formation obtained via the relative actinometric method is dependent on the quencher concentration when photo-oxidations in different solvents are compared; a method to determine the appropriate quencher concentration is described.

Photochemical studies of a photodissociative initiator based on a benzophenone derivative possessing a thioether moiety

Abstract S -(4-Benzoyl)phenylthiobenzoate (BpSBz) and 4-benzoyl-phenyl benzoate (BpOBz) in acetonitrile were photolyzed under steady-state and laser-flash conditions. Analysis of transients absorptions and final products from the photolysis of BpSBz showed that 4-benzoylphenylthiyl and 4-benzoyl radicals were formed with an initial quantum yield of 0.45. Benzaldehyde was the main final product. In contrast, photolysis of BpOBz did not yield benzaldehyde, and nanosecond laser-flash photolysis of BpOBz showed only a long-lived triplet state. These results suggest that CO bond cleavage does not occur as a primary photochemical reaction of BpOBz. The implications for the use of BpSBz as a photoinitiator of polymerization are discussed.

ROSE BENGAL AGGREGATION IN RATIONALLY SYNTHESIZED DIMERIC SYSTEMS

Abstract— Rose Bengal derivatives (I‐VI) have been synthesized as part of a program to study the spectroscopy of model systems for Hpd dimer. The absorption and emission spectra as a function of solvent are diagnostic for the formation of aggregated conformers. Based on our spectroscopic results we conclude that these compounds exist in open conformation in ethanol and other organic solvents, and that they form intramolecular dimers in aqueous solution.

Micro-organizational control of photochemical oxidations: Rose bengal and derivatives (XV)

Abstract we define a microheterogeneous photo-oxidation to be a photosensitized oxidation reaction whose efficiency is enhanced beyond that of diffusion control by the covalent bonding of a sensitizer to a ligand. The ligand is responsible for enhancing the local concentration of a specific substrate susceptible to reaction with an excited state derived from the proximate sensitizer. We illustrate the principle with several applications in singlet oxygen processes.

PROPERTIES OF ROSE BENGAL: (X) NEW DERIVATIVES OF POLYMER‐ROSE BENGAL

Abstract— Polymer rose bengal derivatives are converted to their C‐6 ammonium salts. The φ1 O2 derived in CH2C12 is a function of the KB of the neutralizing amine.

Microheterogeneous photosensitizers from water-soluble polymers

Abstract Poly(ethylene glycol) has been functionalized with rose bengal and its photochemical properties and spectra studied in solvents ranging from toluene to water. The compound is a microheterogeneous photosensitizer in that the dyes attached to the polymer aggregate in solvents in which they are not normally soluble. This effects both the quantum yield of singlet oxygen formation and the spectral shapes of the dye.

The water-soluble rose bengal derivatives and their spectroscopic behaviours

Abstract The paper presents a series of novel water-soluble derivatives of Rose bengal. Solubility in water of the C-2 Rose bengel esters has been obtained by the attachment of the proper water-soluble moiety to the dye molecule. It is shown that size of the attached molecule has a significiant influence on the spectroscopic properties of the derivatives. The long side chain strongly influences on the position of the absorption λmax and emission spectre. The side chain creates the microenvironment for the molecule to which is attached. This makes it more difficult the diffusion of H3OXXX ions into the dye molecule and causes an apparent decrease of pK value for protonation of phenol group of xanthene residue. These types of derivatives make possible to carry out the photooxidation in water even at low pHs.