Photophysics of a sulfonated 2‐hydroxyphenylbenzotriazole UV absorber in solution and in polymer substrates

The total absorption spectrum of the UV absorber sodium 2‐(2′‐hydroxy‐5′‐methylphenyl) benzotriazole sulfonate (TINS) has been resolved into contributions by two ground‐state forms in acetonitrile‐water solvent mixtures and hydrogen bonding polymer and protein substrates. These two ground‐state species can be assigned to (i) a planar intramolecularly hydrogen bonded form which can undergo the efficient nonradiative energy dissipation process of excited‐state intramolecular proton transfer (ESIPT), and (ii) a fluorescent nonplanar species in which ESIPT is effectively prevented. The mole fractions of each contributing conformer in the polymeric substrates have been estimated. In all the polymer systems studied, a significant proportion of the TINS molecules exist in the nonplanar form and thus may not contribute to photostabilization of the substrate. The proportion of nonplanar molecules varied from 11 to 86% in synthetic polymers and 20 to 41% in protein substrates.