Fluorescent indolium dyes for applications in aqueous halide sensing¯¯part 2: the repeated alkylation of Harmane post quaternisation

The repeated alkylation of Harmane, 1-methyl-9H-pyrido[3,4-b] indole, post quaternisation has been observed during fusion with primary alkyl acid halides. This can be explained by two possible competing mechanisms, the electrophilic addition of alkylating agent to the resonance enamine form of the quaternised product and/or polyester formation between the quaternised product and the primary alkyl acid halide. The mechanisms are supported by 1H NMR, FTIR and mass spectrometry analysis. The possibility for controlling the repeated alkylation in nanometre size silica pores, in essence restricted geometry nanometre size reaction vessels, is discussed.