Controlling dye (Merocyanine-540) aggregation on nanostructured TiO2 films. An organized assembly approach for enhancing the efficiency of photosensitization
Ac. Khazraji et al., Controlling dye (Merocyanine-540) aggregation on nanostructured TiO2 films. An organized assembly approach for enhancing the efficiency of photosensitization, J PHYS CH B, 103(22), 1999, pp. 4693-4700
The anionic cyanine dye Merocyanine 540 (MC540) dissolved in Aerosol-OT (AO
T) solutions of heptane and toluene possesses a significantly higher fluore
scence quantum yield and excited singlet lifetime than the acetonitrile sol
utions of the dye. The difference in the photophysical properties observed
upon incorporation of the dye into the AOT micelles is attributed to the de
crease in the photoisomerization efficiency. The presence of AOT also contr
ols the aggregation and photosensitization behavior of MC540 adsorbed onto
TiO2 semiconductor nanoparticles. MC540 adsorbed onto nanostructured TiO2 f
ilms from acetonitrile solutions contains both the aggregated and monomeric
forms of the sensitizer, while the dye-modified films obtained from AOT/he
ptane solutions contain mainly the monomeric form of the sensitizer. Signif
icant enhancement in the photocurrent generation efficiency has been achiev
ed in photoelectrochemical cells using the AOT encapsulated dye films. An e
lectroactive polymer (poly(4-vinylpyridine)) film cast on the dye-modified
TiO2 electrode has been found to be effective in promoting charge mediation
and minimizing dye desorption from the electrode surface. The incident pho
ton-to-photocurrent generation efficiency (IPCE) exhibited by the monomeric
form (similar to 40%) is nearly five times greater than the corresponding
efficiency of the aggregate form (similar to 8%). The beneficial aspects of
incorporating dyes in organized assemblies for the purpose of suppressing
nonradiative decay of the excited-state sensitizer and minimizing the aggre
gation effects on semiconductor surfaces are discussed.