Photoisomerization Kinetics of Stilbene-Type Fluorescent Whitening Agents

Abstract

Photoisomerization of stilbene-type fluorescent whitening agents (FWAs) is an important process that governs their isomer distributions and photodegradation rates in the aquatic environment. Kinetic expressions relating parameters for singlet excited-state dynamics, photoisomerization, and photodegradation were derived. Picosecond timecorrelated single photon counting and stationary monochromatic irradiation were used to study the fluorescence lifetimes and steady-state isomer ratios of three widely used FWAs in aqueous solution. Fluorescence lifetimes decrease and Z/E-isomer ratios increase with increasing temperature, which can be interpreted in terms of an activated rate process in the first excited singlet state of the E-isomer having an activation energy of 20-26 kJ mol -1 . The data obtained in the laboratory enable prediction of the FWAs isomer distributions as a function of temperature and under various irradiation conditions in sunlit freshwaters.

Simple Measurement of 4,4’-bis(2-sulfostyryl)-biphenyl in River Water by Fluorescence Analysis and Its Application as an Indicator of Domestic Wastewater Contamination

“…These values correspond to measured values in lake and coastal waters (Hayashi et al, 2002;Kramer, Canonica, Hoigné, & Kaschig, 1996). Photodegradation of FWAs is slowed by the presence of dissolved organic matter, and DSBP was degraded three times faster (t1/2 = 87 min) than DAS1 (t1/2 = 278 min) in lake water under summer noon sunlight (Canonica et al, 1997).…”

“…A simulation study for FWAs photoisomerization in fresh water showed that the E,Eisomer fraction of DSBP was 75%-86% and E-isomer fraction of DAS1 was 7%-18% (Canonica, Kramer, Reiss, & Gygax, 1997). These values correspond to measured values in lake and coastal waters (Hayashi et al, 2002;Kramer, Canonica, Hoigné, & Kaschig, 1996).…”

Photoisomerization of Triazine-stilbene Fluorescent Brighteners in Solution and in their Copolymers with Styrene

“…One of the major photoreactions causing loss of fluorescence is trans(e) -*• cis(z) isomerization, a reaction which involves rotation of the stilbene molecule around the central ethylene bond [14][15][16], The photochemical process of trans-cis isomerization is illustrated in Scheme 2. The mechanism of the emissionless deactivation of the singlet state FBs is in fact a conformation transition of a singlet excited state of the trans isomer being in the eis form accompanied by a well pronounced non-radiative emission -*• S 0 .…”

Environmental impact on the light and perspiration stability of triazinylstilbene fluorescent brighteners on cotton fabrics

“…The photo-induced hydrolyzation and trans-cis photoisomerization of TFBs on cotton fabrics as shown in Schemes 2 and 3 always exist from the beginning of illumination to the end of moisture volatilization [4,8,[26][27][28][29][30].…”