The effect of OH -concentration on the fade rate can be understood by considering the disproportionation reaction of DHAQ 4-. As shown in Scheme 1, 4 moles of OH -are formed when two moles of DHAQ 4-disproportionate. At elevated OH -concentration, the equilibrium shifts to the left, favoring DHAQ 4-over the formation of DHA. Scheme 1: Disproportionation reaction of DHAQ