Exciton Dynamics in the J-Aggregates of a Carbocyanine Dye

We report on the exciton dynamics in the J-aggregating dye 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine, which is known readily to form J-aggregates, even at room temperature and at a low concentration. We performed a series of time-correlated single-photon-counting experiments at different emission wavelengths and at different temperatures in the range between 1.5 and 125 K. Additionally, the temperature dependence of the relative fluorescence quantum yield was determined

Low temperature exciton-exciton annihilation in amphi-PIPE J-aggregates

The mobility of optically excited excitons on J-aggregates can be demonstrated by the phenomena of exciton-exciton annihilation. In this intensity-dependent process the collision of two excitons results in their annihilation and hence in a shortening of the mean excitation lifetime. By measuring the intensity-dependent fluorescent lifetime in contrast to the predicted immobilization of the excitons at low temperature we could prove the excellent mobility of the excitons at a temperature (4K), which is far below their expected freezing point

Nonlinear resonance reflection from and transmission through a dense glassy system built up of oriented linear Frenkel chains: two-level models

A theoretical study of the resonance optical response of assemblies of oriented short (as compared to an optical wavelength) linear Frenkel chains is carried out using a two-level model. We show that both transmittivity and reflectivity of the film may behave in a bistable fashion and analyze how the effects found depend on the film thickness and on the inhomogeneous width of the exciton optical transition.Comment: 26 pages, 9 figure

Nanoscale control of Ag nanostructures for plasmonic fluorescence enhancement of near-infrared dyes

Potential utilization of proteins for early detection and diagnosis of various diseases has drawn considerable interest in the development of protein-based detection techniques. Metal induced fluorescence enhancement offers the possibility of increasing the sensitivity of protein detection in clinical applications. We report the use of tunable plasmonic silver nanostructures for the fluorescence enhancement of a near-infrared (NIR) dye (Alexa Fluor 790). Extensive fluorescence enhancement of ∼2 orders of magnitude is obtained by the nanoscale control of the Ag nanostructure dimensions and interparticle distance. These Ag nanostructures also enhanced fluorescence from a dye with very high quantum yield (7.8 fold for Alexa Fluor 488, quantum efficiency (Qy) = 0.92). A combination of greatly enhanced excitation and an increased radiative decay rate, leading to an associated enhancement of the quantum efficiency leads to the large enhancement. These results show the potential of Ag nanostructures as metal induced fluorescence enhancement (MIFE) substrates for dyes in the NIR “biological window” as well as the visible region. Ag nanostructured arrays fabricated by colloidal lithography thus show great potential for NIR dye-based biosensing applications

Exciton Dynamics in the J-Aggregates of a Carbocyanine Dye

We report on the exciton dynamics in the J-aggregating dye 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine, which is known readily to form J-aggregates, even at room temperature and at a low concentration. We performed a series of time-correlated single-photon-counting experiments at different emission wavelengths and at different temperatures in the range between 1.5 and 125 K. Additionally, the temperature dependence of the relative fluorescence quantum yield was determined.

Photophysical properties of cyanine dyes in sol-gel matrices

Abstract Planar and twisted cyanine dyes with different pK a values are examined concerning their protonation equilibrium in sol-gel matrices. In the sol-gel matrix the equilibrium between the cation and the dicationic form shifts to the dication pointing to acid-base reactions of sol-gel walls with cyanirie dyes. The colorless dicationic species is not found for pseudoisocyanine and in sol-gel bulks prepared with drying control chemical agents (DCCA) indicating the absence of the responsible interaction. The fluorescence lifetimes of cyanine molecules are used to compare the pore size and distribution in sol-gel matrices prepared with and without DCCA. J-aggregation, examined for one dye, depends strongly on environment polarity and pore size

SLOWMOVE - A numerical model for the propagation of slow-moving landslides: issues and theoretical concepts

Gravitational flows characterized by low velocities represent widely-spread and costly geological hazard and pose particular challenges for the development of a representative numerical model. In many cases their behavior depends on complex mechanical and fluid interactions. The development of a physical-based numerical simulation that allows for an accurate model of observed landslide motion is particularly challenging and underlies a number of assumptions and simplifications. Many conventional techniques do not take hydromechanical effects into account or include the inertia of the moving mass which may result in an overestimation of velocities of the flowing materials