The photofading mechanism of commercial reactive dyes on cotton

The photofading mechanism of 16 commercial dyes (8 Procion, 8 Remazol) reactively dyed on cotton is investigated. All 16 dyes fade at similar rates, with DeltaE's of 2.7-6.1 after 15 h irradiation in simulated Florida sunlight. By removal of UV, it is shown that fading is caused by both visible and UV light, with visible light being the dominant factor for azo dyes and UV for phthalocyanines. By removal of oxygen, it is shown that oxygen is critical for fading by visible but not UV light. Quenching experiments with DABCO show that singlet oxygen is unimportant, and therefore the key reaction in visible fading is an electron transfer from the excited state of the dye to oxygen. Water in the pH range 3-8 increases fading by only 36% compared to dry and at more extreme pH's, larger increases in fading are seen. (C) 2003 Elsevier Ltd. All rights reserved.