Abstract: The quenchings of pyrene fluorescence were studied with tetradecylbenzyldime- thylammonium chloride (Zeph) and benzyltrimethylammonium bromide (TMBA) through their Stern-Volmer plots. Transient and steady state fluorescence experiments indicated that the quenching was dynamic and the quenching rate constant (k_q) of Zeph was much larger than that of TMBA with a ratio of 23.2. Theoretical calculations based on conductance measurement and the full-anti configuration of quencher molecule showed that the k_q of TMBA was larger than that of Zeph with a ratio of 2.29 and 1.85, respectively, which were opposite to the experimental results. Coilin of the long alkyl chain in Zeph molecule and the hydrophobic interaction between pyrene and the coiled microenvironment were considered as the causes for the contradiction between experimental results and theoretical calculations.

Key words: Fluorescence quenching, Alkylbenzylammonium, Pyrene, Conductance, Long-chain molecule conformation