Non-radiative pathways of anilino-naphthalene sulphonates: Twisted intramolecular charge transfer versus intersystem crossing

Abstract

The effect of solvent polarity and external heavy atom (ethyl iodide) on the fluorescence properties of 2-tolouidino-6-naphthalene-sulphonate (TNS) and 1-anilino-8-naphthalene-sulphonate (ANS) have been studied. For ANS with rise in polarity, a monotonic decrease of fluorescence yield (αf) and lifetime (τf) is observed while ethyl iodide was found to have negligible effect. For TNS at low polarity αf and τf are found to increase with rise in polarity, while ethyl iodide causes a decrease in τf. At high polarity [ET(30) > 51] behaviour of TNS is more or less similar to that of ANS. It is proposed that polarity-dependent, twisted intramolecular charge transfer is the main non-radiative process for ANS at all polarities [ET(30) = 36-63] and for TNS only at high polarity. At low polarity intersystem crossing is the main non-radiative pathway for TNS. © 1992.