Photoexcitation energy transfer of binary and ternary systems mediated by a bilayer membrane containing biphenyl moiety

Abstract

Intermolecular Forster-type excitation energy transfer has been investigated in a biphenyl-containing bilayer membrane composed of completely synthetic 4-(4′-dodecyloxybiphenyl-4-yloxy)butyl(trimethyl)ammonium bromide (DBBTAB) amphiphiles. The donor, a biphenyl group, was embedded in the interior of the bilayer membrane. The acceptor, titan yellow, with two negatively charged polar groups, was attracted electrostatically to the positively charged surface of the DBBTAB vesicles. The energy transfer efficiency increased, to up to ca. 80%, with the increase of the content of added titan yellow acceptor. Titan yellow quenched the fluorescence intensity of the biphenyl, which fitted a Stern–Volmer plot from which the rate constant for the quenching, K_q, was calculated to be 3.05 × 10¹³ dm³ mol^–1 s^–1. Energy transfer from the titan yellow donor to the fluorescein sodium salt acceptor, both bound to the surface of the DBBTAB membrane, was also observed. Once again, this transfer produced a Stern–Volmer quenching plot, from which the second-order rate constant, K_q, was determined to be 8.53 × 10¹³ dm³ mol^–1 s^–1. The second-order rate constant for the energy transfer, k^′_ET, was calculated to be 1.25 × 10¹³ dm³ mol^–1 s^–1. The agreement between K_q and k^′_ET values suggests that energy transfer to fluorescein sodium salt is responsible mainly for quenching the fluorescence in the DBBTAB vesicles. Furthermore, sequential energy transfer from biphenyl cascading through titan yellow to fluorescein sodium salt was observed in the vesicles. The efficiency of the sequential energy transfer was found to be higher than that obtained from direct excitation of titan yellow in the same vesicular solution. This is rationalized by considering the higher efficiency for photon absorption of titan yellow from biphenyl in the membrane than from direct excitation of the source or direct energy transfer from the biphenyl to the fluorescein sodium salt.