Photoinduced electron transfer across a molecular wall: coumarin dyes as donors and methyl viologen and TiO2 as acceptors.
Coumarins C-153, C-480, and C-1 formed 1:2 (guest:host) complexes with a water-soluble cavitand having eight carboxylic acid groups (OA) in aqueous borate buffer solution. The complexes were photoexcited in the presence of electron acceptors (methyl viologen, MV(2+), or TiO(2)) to probe the possibility of electron transfer between a donor and an acceptor physically separated by a molecular wall. In solution at basic pH, the dication MV(2+) was associated to the exterior of the complex C-153@OA(2), as suggested by diffusion constants (~1.2 × 10(-6) cm(2)/s) determined by DOSY NMR. The fluorescence of C-153@OA(2) was quenched in the presence of increasing amounts of MV(2+) and Stern-Volmer plots of I(o)/I and τ(o)/τ vs [MV(2+)] indicated that the quenching was static. As per FT-IR-ATR spectra, the capsule C-153@OA(2) was bound to TiO(2) nanoparticle films. Selective excitation (λ(exc) = 420) of the above bound complex resulted in fluorescence quenching. When adsorbed on insulating ZrO(2) nanoparticle films, excitation of the complex resulted in a broad fluorescence spectrum centered at 500 nm and consistent with C-153 being within the lipophilic capsule interior. Consistent with the above results, colloidal TiO(2) quenched the emission while colloidal ZrO(2) did not.
Department of Chemistry, University of Miami, Coral Gables, Florida 33124, USA.
Mintu
M
Porel
Agnieszka
A
Klimczak
Marina
M
Freitag
Elena
E
Galoppini
V
V
Ramamurthy
D003102:Colloids; D004396:Coloring Agents; D003374:Coumarins / Q000737:chemistry*; D004579:Electron Transport; D005453:Fluorescence; D010269:Paraquat / Q000737:chemistry*; D055668:Photochemical Processes; D014025:Titanium / Q000737:chemistry*
D003102:Colloids; D004396:Coloring Agents; D003374:Coumarins; C009495:titanium dioxide; D014025:Titanium; D010269:Paraquat