Molecular architecture in cyanine dye aggregates at the air-water interface. Effect of monolayer composition and organization on fluorescent behavior

Abstract

The fluorescence behavior of an amphiphatic oxacyanine dye and its thiacyanine analogue has been investigated in spread monolayers at the air-water interface. J-aggregate formation as a function of area/(dye molecule) was monitored by spectral changes in pure dye monolayers and in 1:1 mixtures of dye with various fatty acid coaggregates. Simultaneously, the thermodynamic behavior of these systems was characterized by the associated surface pressure-area isotherms. In all cases, J-aggregate formation may be related to a phase transition in the isotherm. The intensity of aggregate fluorescence is found to be inversely related to the work, AW, of compression of the monolayer through the transition. Inclusion of the fatty acid coaggregate was shown to facilitate J-aggregate formation in the order stearic > elaidic > oleic. Both fluorescence and thermodynamic data indicate more extensive aggregate formation in the thiacyanine systems. Aside from the paramount role played by the chromophore-chromophore interactions in determining J-aggregate phenomena, this study suggests important contributions from dispersion forces involving the long hydrocarbon moieties.

Effects of molecular organization on photophysical behavior: lifetime and steady-state fluorescence of chlorophyll a singlets in monolayers of dioleoylphosphatydylcholine at the nitrogen-water interface

“…of the constituents occurs. 13,21,22 The concentration for half-quenching (4.55 ± 0.1 1012 molecules/cm2) is not dramatically different from that reported by Costa et al (4.3 X 1012 molecules/cm2) in transferred phytol monolayers as well as that given by Tweet et al in oleoyl alcohol mentioned above.3,5 (Applying eq 1 to their data gives C0 ~4.0 X 1012 molecules/cm1 2.) The fit of both kinds of Chi a data to a close second-order dependence on concentration over the range of these measurements indicates the dominance of trapping involving statistical pairs of molecules, as has long been suggested.19 However, the agreement in C0 between the two types of measurements suggests the dominance of a dynamic process, either by diffusion of the excited molecule to a trap or migration of the exciton among molecules in the array.…”

J-aggregates of thiacyanine dye organized in LB films: Effect of irradiation of light

“…It is interesting to mention in this context that S. Vaidyanathan et al [47] reported the enhancement of contact and aggregate formation of cationic cyanine dyes by mixing oppositely charged coaggregate. Where oppositely charged coaggregate decreases the charge repulsion between the dye chromophore.…”

Aggregation and structural study of the monolayers formed by an amphiphilic thiapentacarbocyanine

“…2.5 nm. 20 This energy-transfer reaction together with the broad and infrared-shied absorption spectrum of the OTCC aggregates prove that these lms might be integrated in molecular electronic devices, as light emitting diodes or solar cells.…”