Excited-state dynamics of polymer-bound J-aggregates

Abstract

The excited-state dynamics of polymer-bound J-aggregates formed in aqueous mixtures of pseudoisocyanine (PIC) chloride and poly(viny1 sulfonic acid sodium salt) (PVS) (MW -1 1 200) have been studied by picosecond time-correlated single-photon counting and picosecond polarized pump-probe spectroscopy. At a concentration of 40 NM PIC and 5 X 10-4 g/dL PVS, the absorption spectrum of the J-aggregate is characterized by a J-band at 565 nm with a fwhm of ~5 0 0 cm-I. For this particular mixture, a dye molecule is bound to each of the so3groups on the polymer chains. The physical size of the aggregate is therefore determined by the number of polymer residues (-87) per chain. The fluorescence lifetime and fluorescence quantum yield of these J-aggregates are 17 f 3 ps and 0.022 f 0.003, respectively. The lifetime is independent of the excitation intensity. From an analysis of the photophysical parameters, we infer a coherence size of -5 f 1, which is smaller than the physical size of the aggregate. The pump-probe signal at 565 nm is entirely due to bleaching and consists of a fast component, with a decay time comparable to the fluorescence lifetime, and a slow component. The decay kinetics of the induced bleaching are independent of the excitation intensity. The signal at 558 nm consists of an absorption component at early times and a slowly decaying bleaching component at long times. The anisotropy at 565 nm was constant over the 160-ps time range of the signal. The kinetics are rationalized in terms of a model involving the singlet exciton states of the J-aggregate and a long-lived bottleneck state. The induced absorption at early times for excitation on the blue edge of the J-band is consistent with a one-exciton to two-exciton transition.

Metal-Enhanced Fluorescence of Pseudoisocyanine J-Aggregates Formed in Layer-by-Layer Assembled Films

“…16,42 The observed decrease of the PIC J-aggregate quantum yield in the LbL film should correlate with the fluorescence decay time. 16,42 Indeed, Figure 1c shows the significant difference in the fluorescence decay curve profiles for the J-aggregates in the solution and LbL film. In the aqueous solution, the monoexponential decay was obtained with lifetime τ sol ∼ 1.39 ± 0.01 ns (Figure 1c, blue curve).…”

Spacer-Controlled Aggregation and Surface Morphology of a Selenacarbocyanine Dye on Gemini Monolayers

“…1 Since its discovery by Jelly 2 and Scheibe, 3 much attention has been paid to the J-aggregate from their structural features, 4-7 photographic process 8,9 nonlinear optical properties, 10,11 and multiple wavelength optical recording materials. 12 J-aggregates of cyanine dyes have been assembled in aqueous solutions, 2,3 in silver halide emulsions, 13,14 in solutions containing polyelectrolyte or salt, 15,16 and in films. [17][18][19][20] Since the J-aggregate is generally regarded as resulting from the interaction of large numbers of molecules in an orderly array, monolayer and Langmuir-Blodgett techniques, which provide excellent ways of controlling molecular arrangement, 21,22 have been widely used for the study of two-dimensional aggregation of dyes.…”

Fluorescence quenching in tip-enhanced nonlinear optical microscopy

“…2 However, TENOM has primarily been used for the study of molecularly aggregated systems for which fast energy transfer relaxes excitation energy large distances from the probe. 3,4 Fast energy transfer therefore mitigates the effects of fluorescence quenching by the gold or silver probes in these experiments.…”