The term solvatochromism is used to describe the changes in the optical properties of a dye molecule by influence of the solvent characteristics. Solvatochromic shifts are governed by intermolecular interactions between solute-solvent that can be either electrostatic (non-specific interactions) or chemical (specific interactions). Due to the complexity of these interactions and absence of theoretical models that can explain the specific effects of solvent, different authors have introduced empirical parameters to building more reliable solvent polarity scales. Out of various polarity scales that have arisen from this need, those based on the effect of solvent polarity on the electronic excitation energy of indicator organic dyes are the most prevalent in literature. The use of empirical equations that correlate bathochromic (positive solvatochromism) and hypsochromic (negative solvatochromism) shifts of optical spectra of organic molecules with the polarity of solvent has become essential for understanding solute-solvent interactions. This review article presents main mathematical equations that use linear correlations between macroscopic and/or microscopic polarity functions of solvent with spectroscopic parameters of solute (dye) in construction of solvent polarity scales. In addition, main mathematical models that use solvatochromic shifts to estimate the dipole moment of ground and excited state are discussed.

Abstract Damage resulting from the incidence of ultraviolet (UV) radiation on the skin is common nowadays, with UVB (290-320 nm) and UVA (320-400 nm) radiation responsible for photoaging, sunburn and carcinogenesis. For this reason, sunscreens represent products of growing interest to prevent such damage. However, there are few organic filters marketed worldwide with photostability and effectiveness at wavelengths greater than 340 nm (long UVA), which justifies the exploration for new compounds. In this work, we determined the photostability and sun protection factor (SPF) of three 2-(2’-hydroxyphenyl)benzoxazole derivative dyes in order to develop new organic UV filters. UV-vis spectrophotometry has high level of reproducibility when compared with in vivo human clinical methods. Solubility determinations were performed in different solvents. The compounds absorbed UVA and UVB radiation, with maximum absorption wavelengths ranging from 336 to 374 nm. Photostability was evaluated using a solar simulator (3 J.m2.s-1 UVA radiation) for a maximum of 3 h. The 2-(amino-2’-hydroxyphenyl) benzoxazoles showed higher photostability than the acetylated derivative under the evaluated conditions. The three benzoxazoles presented SPF values of around 40 and preliminary results indicate that they show suitable properties to act as good chemical filters in photoprotective formulations.