GROUND AND EXCITED-STATES ACID-BASE PROPERTIES OF ACRIDINE-1,8-DIONE DYES

The acid-base properties of an interesting and important bifunctional group of compounds, acridinedione dyes, were studied in a 95:5 water-m ethanol mixture. The dyes exist in neutral, deprotonated and protonate d forms in equilibrium at appropriate acid-base conditions. The neutra l form of the dyes absorbs around 380-400 nm and emits around 340-460 nm in the water-methanol mixture. The deprotonated form of the dyes ab sorbs around 450-470 nm and emits around 500-520 nm. The protonated fo rm of the dyes absorbs around 410-430 nm and emits around 470-500 nm. The pK(a), values are calculated using Forster's and fluorimetric tit ration methods. The variation of the enhancement in the fluorescence i ntensity and lifetime of the protonated and deprotonated form of the d yes with substituent are discussed. The influence of substituent on th e pK(a), and pK(a) values are discussed. The dyes are more acidic in the excited state when compared to the ground state. The fluorescence lifetime of the neutral form is around 6.0-9.0 ns and that of the prot onated and deprotonated forms of the dye is 3.0-6.0 ns. (C) 1997 Elsev ier Science S.A.