Investigations of Energy Migration in an Organic Dendrimer Macromolecule for Sensory Signal Amplification

Abstract

The issue of macromolecular exciton delocalization length and fluorescence sensing of energetic materials is investigated and modeled from results of nonlinear optical and time-resolved spectroscopy. By using two- and three-photon absorption techniques the fluorescence quenching effects of an organic dendrimer for sensing TNT were carried out. The Stern-Volmer plots for the set of dendrimers were examined and a large quenching constant for the dendrimer G4 was obtained (1400 M(-1)). The quenching constant was found to increase with the dendrimer generation number. The mechanism for the enhanced sensitivity of the dendrimer system was examined by probing the exciton dynamics with femtosecond fluorescence up-conversion. Fluorescence lifetime measurements revealed a multicomponent relaxation that varied with dendrimer generation. Fluorescence anisotropy decay measurements were used to probe the exciton migration length in these dendrimer systems and for the large structure the excitation migration area covers approximately 20 units. All of these results were used in a model that describes the exciton localization length with the fluorescence quenching strength. The use of time-resolved techniques allows for a closer and more detailed description of the mechanism of sensory amplification in organic macromolecules.

Fluorescent Phosphorus Dendrimer as a Spectral Nanosensor for Macrophage Polarization and Fate Tracking in Spinal Cord Injury

“…Dendrimers are represented by multiple subclasses depending on their chemical composition—thus, the subclass of phosphorus dendrimers is defined by the presence of at least one phosphorus atom at each branching point. Branched moieties can be broadly modified to shape the key biochemical properties of dendrimers depending on the desired application, such as surface charge, peptide‐based targeting, or fluorescence when fluorophores are incorporated in their structure . The presence of numerous surface groups (charged or modified as necessary) and a hydrophobic core allows for a high drug payload and multifunctionality, conferring also the ability to transport therapeutic cargos across various cell membranes or biological barriers via cellular internalization .…”

Dendrimer sensors

“…57 Due to the large two-photon absorption cross-sections of the high-generation dendrimers, fluorescence quenching could be stimulated under near-IR irradiation. 56,57 The dynamics of fluorescence anisotropy decay on the picosecond timescale revealed that closer packing of the surface groups in the higher generation dendrimers allowed effective migration of the excitons around the dendrimer surface to a quenching site. 56 This amplified the fluorescence quenching effect for higher generations in an analogous manner to the molecular wire effect of amplifying fluorescent polymers.…”

“…56,57 The dynamics of fluorescence anisotropy decay on the picosecond timescale revealed that closer packing of the surface groups in the higher generation dendrimers allowed effective migration of the excitons around the dendrimer surface to a quenching site. 56 This amplified the fluorescence quenching effect for higher generations in an analogous manner to the molecular wire effect of amplifying fluorescent polymers. It was hypothesised that porous films of these materials would make effective solid state sensors for explosive vapours but at the time of writing this had not been reported.…”

“…From the data collected it is not clear whether this represents a strong binding interaction by the acetylene moieties for the aromatic analytes but based on the rapid photodegradation of the films it is likely that the presence of the analytes is Traditionally solution-based quenching has been used to screen the potential for new fluorophores to act as effective sensing elements. 25,31,33,56,68,172 However, it has been seen that a high quenching constant in solution does not guarantee a strong thin film response and these are most…”

Poly(dendrimer)s for explosives sensing

“…A larger reflects a stronger fluorescence quenching response. This relatively straightforward method has been used to investigate the quenching ability of a wide range of explosive analytes and taggants with a variety of materials such as small molecules 50,51 , dendrimers 52,53 , functionalized nanoparticles 54,55 , and polymers 49,56 . Solution quenching measurements of these materials, using paraquat as the analyte, yielded values that were 2.6 to 65 times larger than that of the monomeric receptor 3.1 (1630 M -1 ).…”