Dyes and Pigments: New Research Edited by Arnold R. Lang

CONTENTS

PREFACE
Chapter 1 – Photodynamic therapy (PDT) is a cancer treatment based on activation of a drug by light. The drug, called photosensitizer, absorbs the energy of light of the proper wavelength and transfers it to surrounding molecules, mainly oxygen, forming reactive oxygen forms like radicals and singlet oxygen. These highly reactive species are responsible for destruction of targeted cells. Besides the direct effect on the cells, vascular shutdown develops as well and immune response is activated, both being important for long-term control over the tumor. Most of the photosensitizers are recruited from the group of porphyrins and related compounds like chlorins, bacteriochlorins, porphycenes, texaphyrins, and phthalocyanines. However, other dyes also entered the trials for photodynamic evaluation, e.g. some tricyclic dyes or hypericine. We discuss in this chapter, the history, photophysical and photochemical principles of PDT, as well as the biological effects of the photosensitizers. The main structural groups of photosensitizers are discussed and the most important drugs, either approved or in trials are described. Also, other approaches closely connected with PDT (catalytic therapy, sonodynamic therapy, photothermal therapy, and photochemical internalisation) are mentioned in this chapter.

Chapter 2 – Phthalocyanine analogues containing alkyl-substituted benzenoid rings and pyridine rings are interesting compounds, because quaternation of the pyridine nitrogen is expected to form cationic amphiphilic compounds.

Non peripheral long alkyl substituted zinc phthalocyanine derivatives, zinc bis(1,4- didecylbenzo)-bis(3,4-pyrido)porphyrazine and zinc bis(1,4-didecylbenzo)-bis(2,3- pyrido)porphyrazine were reacted with dimethyl sulfate and monochloroacetic acid to give their quaternary products. Also the zinc phthalocyanine derivatives reacted with diethyl sulfate to afford the sufo-substituted products. All reacted compounds showed amphiphilic character.

Regio isomers of zinc bis(1,4-didecylbenzo)-bis(3,4-pyrido)porphyrazine were also quaternized with dimethyl sulfate.

Identical peaks in cyclic voltammograms appeared for these products before and after quaternization.

Zinc bis(1,4-didecylbenzo)-bis(2,3-pyrido)porphyrazine was evaluated the the photodynamic therapy of cancer efficacy by cancer cell culture. The light exposed dimethyl sulfate quaternized zinc bis(1,4-didecylbenzo)-bis(2,3- pyrido) porphyrazines in IU-002 cells produces cell disruption that can be detected as a decrease as fluorescence.

Chapter 3 – The textile industry uses large amounts of water in its dyeing processes. Due to environmental problems the supercritical dyeing process has been developed. In this process supercritical carbon dioxide is used as the solvent for dyes.

On the other hand, pigments, used in the formulation of paints, inks, toners and photographic emulsions can be micronized by supercritical antisolvent process. Their production in form of micrometric particles with controlled particle size distribution can largely improve their characteristics.

For these reason, in the last years, supercritical fluids more and more have been proved as environmentally benign media for dyeing processes and as antisolvent to control the formation of micrometric particles.

The physico-chemical properties of supercritical fluids are halfway between those of gases and liquids; more these properties can be easily modified by a simple variation of pressure or/and temperature. Therefore, supercritical fluids can be used to develop solventless or solvent reduced processes and their mass transfer properties are useful to produce micronized particles with controlled size and distribution.

In this field, the publications appeared over the past years could be reviewed under two groupings, one involving the measurements of solubilities of dyes in supercritical carbon dioxide, with and without co-solvent, and supercritical CO2 dyeing of fibre, and the other involving the micronization of dyes with narrow particle size distribution using a supercritical antisolvent process. In the following, a lot of recent papers will be cited, which should give an overview of actual results on solubility and precipitation of dyes in supercritical carbon dioxide.

Chapter 4 – Photochromism refers to a reversible phototransformation of a chemical species between two forms having different absorption spectra. Photochromic compounds reversibly change not only the absorption spectra but also their geometrical and electronic structures. The molecular structure changes induce physical property changes of the molecules, such as fluorescence, refractive index, polarizability, electrical conductivity, and magnetism. When such photochromophores are incorporated into functional molecules, such as polymers, host molecules, conductive molecules, liquid crystals, the properties can be switched by photo irradiation. Among of all kinds of photochromic compounds, the spirooxazine dyes (SPO) are well-known photochromic compounds that show their high fatigue resistance and excellent photostability, which is one of the most promising candidates for applications in molecular electronics such as optical memory, molecular switching devices. In this review, we describe the recent development of spirooxazine dye as photocontrolled molecular switches in molecular materials, especially photochromism of spirooxazine in single crystal phase, spirooxazine dye polymer materials as fluorescence molecular switches, electrical conductivity switches, and viscosity switches, liquid crystal switches, gel switches and so on. In addition, layer by layer self–assemble spirooxazine dye in supermolecular chemistry as a photoswitching unit is described. We mainly present specific examples from our own research, which highlight our research group’s contribution.

Chapter 5 – Dyestuff in water introduces several environmental problems and should be removed for clean water system. Fenton oxidation can be as an effective technique for the water treatment. In this report, homogeneous and heterogeneous catalysis in Fenton oxidation was examined for two dyes with acidic (Naphthol blue-black, NBB) and basic (Methylene Blue, MB) properties. The behaviour of these dyes under different experimental conditions (temperature, pH, peroxide concentration, Fe concentration) was studied using Fenton (Fe2+) and Fenton-like (Fe3+) reactions for the following processes: 1) normal Fenton oxidation, 2) Fenton oxidation combined with sonication effect, 3) Fenton oxidation combined with a solid catalyst (activated carbon). The main Fenton oxidation reactants, Fe2+, Fe3+ and H2O2 were used in small quantities in order to observe closely the reaction kinetics for decolourisation of these dyes. It was found that both sonication and heterogeneous catalysis offer improvements to the Fenton oxidation under optimised conditions, with Fe2+ being faster than Fe3+ initially but Fe3+ ending up with a higher overall efficiency. 90-95% decolourisation was achieved in some optimised runs after 2 hours; however the general decolourisation was completed for all batch runs after a period of 24 hours, except in conditions where the reaction did not proceed at all. Chemical oxygen demand (COD) removal also occurred during the decolourisation process of both dyes, in maximum efficiencies of about 80% after 48 hours. Methylene blue also showed greater decolourisation efficiency in comparison with Naphthol blue-black for most of the experimental runs under the same experimental conditions. The reaction kinetics was mainly pseudo-first order for majority of the homogeneous reaction, as determined by non-linear regression or a combination of first order kinetics for heterogeneous reactions.