Probing the donor and acceptor dye assemblies at the galleries of alpha-zirconium phosphate

Self-assembly of fluorescein (Fl) and rhodamine B (RhB) dyes at the galleri es of surfactant impregnated a-zirconium phosphate (SAZrP) is demonstrated here. Cationic surfactants, cetyltrimethylammonium bromide and didodecyldim ethylammonium bromide solubilize the hydrophobic dyes in aqueous solutions and enhance their binding to negatively charged alpha -ZrP. Fl molecules im mobilized in SAZrP exhibit distinct spectroscopic signatures with 14 nm red shifted absorption (lambda (max) at 501 nm vs 487 nm in aqueous solutions) and hyperchromicity (epsilon (max) = 100,000 M-1 cm(-1) twice the value in aqueous or micellar solutions). RhB, in contrast, retains the spectroscopic features as those observed in aqueous solutions (lambda (max) at 553 nm). Enhanced relative quantum yields for the SAZrP bound dyes as compared to aq ueous solutions are observed (phi (rel) values of 1.7 and 1.32 for Fl/CAZrP and RhB/CAZrP respectively). Facile binding of Fl molecules with SAZrP was used to investigate the energy transfer between co-immobilized Fl (donor) and RhB (acceptors) molecules. Quenching of Fl fluorescence by RhB, immobil ized on SAZrP was efficient and Stern-Volmer quenching constants (K-SV) on the order of 10(6) M-1. Energy transfer efficiencies are enhanced an order of magnitude when compared to solution phase values. Fluorescence polarizat ion of the Fl/SAZrP assemblies at varying Fl concentrations indicated depol arization of the emission at high loadings. Quenching rate constants increa sed with the dye loading and fluorescence lifetimes decreased due to self-q uenching (tau = 3.75 ns (monoexponential), low loading vs tau (1) = 0.44 ns (69%, biexponential), high loading). Donor to donor energy migration is po ssible within these assemblies. Accelerated energy transfer of the immobili zed dyes will be useful in the design of artificial light harvesting comple xes and photon antennas. (C) 2000 Elsevier Science B.V. All rights reserved .