New fluorescent quinolinium dyes - applications in nanometre particle sizing

Bromide, iodide and tetraphenylborate quaternary salts of four new highly f luorescent dyes have been produced by the reaction of the 6-methoxyquinolin e heterocyclic nitrogen base with 3-bromo-1-propanol, methyl iodide and met hyl bromide with one of the dyes having its counter-ion exchanged for the t etraphenylborate ion. Three of the dyes, unlike the base, are readily water soluble, the tetraphenylborate salt only slightly water soluble and all ar e fluorescent over a broad pH range. The dyes have been characterised in te rms of their water solubility, their steady-state fluorescence spectra and their bi-exponential fluorescence lifetimes, which are all found to be in t he range approximate to 10-30 ns. We have found that the cationic dyes read ily bind to negatively charged colloidal silica particles and because of th e suitably long fluorescence lifetimes we have been able to determine the p article size of Du Pont's SM30 colloidal silica using time-resolved fluores cence anisotropy. The average particle diameter, determined using three of the dyes, was 6.8 +/- 0.6 nm, which compares well with Du Pont's mean value of 7 nm. (C) 1999 Elsevier Science Ltd. All rights reserved.