DETERMINATION OF GROUND AND EXCITED STATES DIPOLE MOMENTS OF EOSIN B DYE BY SALVATOCHROMIC SHIFT METHOD

 

We live in a colourful world, the preparation and use of dyestuffs is one of the oldest human activities. With the advent of the industrial revolution, chemistry began to play a prominent role in the improvement of the existing colorants and their applications. Among the groups of organic dyes, the eosin family of dyes constitutes a widely used set of fluorescent stains in modern biology and histology. They are commonly used as probe for the investigation of many chemically important systems, and have been studied extensively both experimentally and ( Zerkerhamidin et at., (2015). effect of solvent on the absorption and fluorescence characteristics of organic compounds has been a subject of extensive research. Excitation of a molecule by photon causes a redistribution of charges leading to conformational changes in the excited state. This can result in increase or decrease of dipole moment of the excited state as compared toground state. The dipole moment of an electronically excited state of a molecule is important property that provides information on the electronic and geometrical structure of themolecule in short –lived state. Knowledge of the excited- state dipole moment of electronically excited molecules is quite useful in designing nonlinear optical materials, elucidatingthe nature of the excited states and in determining the courseof photochemical transformation.(joshi et al.,2012).

Until the 1850s virtually all dyes were obtained from natural sources, most commonly from vegetables, such as plants, trees, and lichens, with a few from insects. Solid evidence that dyeing methods are more than 4,000 years old has been provided by dyed fabrics found in Egyptian tombs. Ancient hieroglyphs describe extraction and application of natural dyes. Countless attempts have been made to extract dyes from brightly coloured plants and flowers; yet only a dozen or so natural dyes found widespread use. Undoubtedly most attempts failed because most natural dyes are not highly stable and occur as components of complex mixtures, the successful separation of which would be unlikely by the crude methods employed in ancient times. Nevertheless, studies of these dyes in the 1800s provided a base for development of synthetic dyes, which dominated the market by 1900.

However, dye is a substance used to impart colour to textiles, paper, leather, and other materials such that the colouring is not readily altered by washing, heat, light, or other factors to which the material is likely to be exposed. Dyes differ from pigments, which are finely ground solids dispersed in a liquid, such as paint or ink, or blended with other materials. Most dyes are organic compounds (i.e., they contain carbon), whereas pigments may be inorganic compounds (i.e., they do not contain carbon) or organic compounds. Pigments generally give brighter colours and may be dyes that are insoluble in the medium employed.(Abrahat et al., 2019).

There are several ways to classify dyes. For example, they may be classified by fiber type, such as dyes for nylon, dyes for cotton, dyes for polyester, and so on. Dyes may also be classified by their method of application to the substrate. Such a classification would include direct dyes, reactive dyes, vat dyes, disperse dyes, azoic dyes, and several more types of dyes. (Gregory et al., 1990)

Eosin is a class of fluorescent red dye. It is an artificial derivative of fluorescein consisting of two closely related compounds, eosin Y and eosin B. Eosin B is a dibromodinitro derivate of fluorescein and has a faint bluish cast. Eosin B performs equally well as eosin Y, and sometimes can give a more brilliant red color.  Eosin B can be used to stain cytoplasm, red blood cells, collagen, and muscle fibers for histological examination. It is most often used as a counterstain to hematoxylin in H&E staining.(lai et al.,2012)

 

Figure 1. structure of Eosin B

alcohols are widely used as a solvent. They are relatively safe and can be used to dissolve many organic compounds that are insoluble in water. They  used, for example, in many perfumes and cosmetics.(rijavec et al.,2007) alcohols used in this work include ;methanol, ethanol, propanol, butanol, and hexanol.

Solvatochromism is a reversible change of the absorption or emission spectrum of a material that is induced by the action of solvents. The colour change is the consequence of the absorption maximum shift, which occurs due to differences between the solvation energy of the initial and excited state in various solvents. The excited state, which is more polar than the initial state, is more stable in more polar solvents. Such systems require lower energy for excitement, which leads to bathochromic shift of the absorption spectrum. This phenomenon is called positive solvatochromism. The less polar excited state than the initial state produces a counter-effect and a hypsochromic shift of the absorption maximum. This phenomenon is called negative solvatochromism. The majority of solvatochromic materials are metal complexes.(Edward et al.,2007).

The study of the determination of ground and excited state dipole moments of eosin B by solvatochromic shift method is Important as it provide analytical information on the ground and excited state dipole moment of eosin B

To estimate the ground and excited dipole moments of Eosin B in some selected solvents by solvatochromismic method.

The scope of a study focused on the determination of ground and excited state dipole moments of eosin B by the solvatochromic shift method typically include the following aspects,

Overall, such a provide a valuable insight into the molecular properties of eosin B and its behavior in different chemical environments, which can have broad implications in various scientific disciplines.