Effect of Concentration on the Photophysics of Dyes in Light‐Scattering Materials.

Abstract

Photoactive materials based on dye molecules incorporated into thin films or bulk solids are useful for applications as photosensitization, photocatalysis, solar cell sensitization and fluorescent labeling, among others. In most cases, high concentrations of dyes are desirable to maximize light absorption. Under these circumstances, the proximity of dye molecules leads to the formation of aggregates and statistical traps, which dissipate the excitation energy and lower the population of excited states. The search for enhancement of light collection, avoiding energy wasting requires accounting the photophysical parameters quantitatively, including the determination of quantum yields, complicated by the presence of light scattering when particulate materials are considered. In this work we summarize recent advances on the photophysics of dyes in light-scattering materials, with particular focus on the effect of dye concentration. We show how experimental reflectance, fluorescence and laser-induced optoacoustic spectroscopy data can be used together with theoretical models for the quantitative evaluation of inner filter effects, fluorescence and triplet formation quantum yields and energy transfer efficiencies.

Photophysics of Xanthene Dyes at High Concentrations in Solid Environments: Charge Transfer Assisted Triplet Formation

“…Even at concentrations for which reabsorption is negligible, red shifts still persist on increasing dye concentration. Concentration‐dependent Stokes shifts, found generally in dyed materials at high concentrations, are attributed to long‐range interactions (at distances higher than 10 nm) between excited dye molecules and neighboring molecules in the ground state . At the highest concentrations, spectra are still affected by reabsorption, though to a lesser extent than for thick layers.…”

“…2 correspond to twice the standard deviation in the excitation interval 500-540 nm for EoY and 535-555 nm for PhB. The remaining decrease has to be attributed to mechanisms other than reabsorption and reemission, namely static quenching due to the absorption of aggregates or virtual traps and to dynamic quenching produced by excitation energy migration to those entities (29).…”

Insights into the Photophysics and Supramolecular Organization of Congo Red in Solution and the Solid State

“…Aggregation behavior is also strongly affected by external (dye environment related) factors such as temperature, pH, concentration of the dye, ionic strength, and solvent polarity. One of the main consequences of the self‐assembly of dyes is that molecular aggregates have distinct photophysical properties compared to the individual monomer . In many cases the strong intermolecular interactions that hold aggregates together are responsible for the weakening of emission (“aggregation‐caused quenching”) and this may severely limit the use of the dyes in real‐world applications such as organic light‐emitting diodes (OLEDs) .…”

Indocyanine green modified silica shells for colon tumor marking

“…Additionally, the near monolayer coatings of dye found on the 100 nm nanoshells as well as their separation by an 8 nm silica shell results in a lower localized dye concentration, which has been shown to reduce the formation of energy traps (aggregates of dye molecules that decay absorbed energy non-radiatively) and thus limit self-quenching. [74,75] Previous studies with higher ICG dye loading than the present nanoshells and microshells have shown a that increasing localized ICG concentration on shells results in severe selfquenching.…”