Quantitative Energy Transfer in Organic Nanoparticles Based on Small-Molecule Ionic Isolation Lattices for UV Light Harvesting

Abstract

Fluorescent nanoparticles based on organic dyes are promising materials for bioimaging applications. Recently, ultrabright fluorescent nanoparticles with orange emission were obtained by hierarchical coassembly of a cationic rhodamine dye with cyanostar anion-receptor to produce small-molecule ionic isolation lattices (SMILES). The cyanostar anion-complexes provides spatial and electronic isolation of the rhodamine dye prohibiting aggregation quenching. Cyanostar also constitutes a UV excitation antenna system to boost the brightness of the rhodamine SMILES nanoparticles due to a large molar absorption coefficient in the UV region and efficient energy transfer to the dye. To further study the UV light harvesting process, we compared the rhodamine SMILES nanoparticles to green emissive cyanine-based SMILES nanoparticles, different in spectral overlap between cyanostar and the dye molecules. The energy transfer efficiency is increased from 80% in rhodamine SMILES to 100% in cyanine SMILES NPs due to increased spectral overlap. The energy transfer process was studied in detail by using femtosecond (fs) transient absorption (TA) spectroscopy, yielding energy transfer time-constants of around 0.4 and 1.3 ps for the cyanine- and rhodamine-based SMILES NPs, respectively. This result correlates well with the spectral overlap integrals and accounts for increased energy transfer and UV light harvesting efficiency. This insight into the UV light energy harvesting processes in the supramolecular SMILES materials will aid future design of ultrabright functional nanomaterials.

Universal Concept for Bright, Organic, Solid-State Emitters─Doping of Small-Molecule Ionic Isolation Lattices with FRET Acceptors

“…Simply adding the anion-binding macrocycle cyanostar (CS) 44 to cationic fluorophores induced predictable packing of the dyes into small-molecule ionic isolation lattices (SMILES, Figure 1A), where cationic fluorophores (green) are efficiently isolated from each other by the large disc-shaped anion complexes formed between anions (orange) and 2 equiv of CS (gray, Figure 1B), as sketched in Figure 1. 45,46 The SMILES concept has been demonstrated for a range of prevalent dye classes in both thin films and crystals, 45 as well as in nanoparticles, 47,48 yielding both very high brightness and high dye density in the solids (up to ∼0.5 M, or one dye per 3.5 nm 3 ).…”

“…Anion-binding receptors offer a supramolecular approach to modify the size, shape, and properties of anions and thus packing of molecular salts. , Taking this direction, we recently introduced a new and simple method to produce bright fluorescent solid-state materials from conventional organic dyes. Simply adding the anion-binding macrocycle cyanostar (CS) to cationic fluorophores induced predictable packing of the dyes into small-molecule ionic isolation lattices (SMILES, Figure A), where cationic fluorophores (green) are efficiently isolated from each other by the large disc-shaped anion complexes formed between anions (orange) and 2 equiv of CS (gray, Figure B), as sketched in Figure . , The SMILES concept has been demonstrated for a range of prevalent dye classes in both thin films and crystals, as well as in nanoparticles, , yielding both very high brightness and high dye density in the solids (up to ∼0.5 M, or one dye per 3.5 nm 3 ).…”

Molecular Nanotechnology for Tomorrow’s World: A Forum Dedicated to Professor Sir Fraser Stoddart on the Occasion of His 80th Birthday

“…Upon tuning, they found that the energy-transfer efficiency could be increased by 100%. 3 Liu et al studied an interesting phenomenon of ligand-induced transformation of CsPbBr 3 nanocrystals to nanowires for applications as X-ray photodetectors, where the photodetectors fabricated using the obtained CsPbBr 3 nanowires displayed enhanced photocurrents. 4 In another work, Beton and coauthors achieved submolecular resolution imaging based on P 3 HT:PCBM films, showing a promising application potential in organic photovoltaic devices.…”

“…Laursen et al quantitatively investigated the energy transfer in small-molecule self-assembled nanoparticles for harvesting UV light. Upon tuning, they found that the energy-transfer efficiency could be increased by 100% . Liu et al studied an interesting phenomenon of ligand-induced transformation of CsPbBr 3 nanocrystals to nanowires for applications as X-ray photodetectors, where the photodetectors fabricated using the obtained CsPbBr 3 nanowires displayed enhanced photocurrents .…”

A Universal Concept for Bright, Organic Solid State Emitters - Doping of Small Molecule Ionic Isolation Lattices with FRET Acceptors

“…Simply adding the anion-binding macrocycle cyanostar (CS) 43 to cationic fluorophores induced predictable packing of the dyes into small-molecule ionic isolation lattices (SMILES, Figure 1A), where cationic fluorophores (green) are efficiently isolated from each other by the large disc-shaped anion complexes formed between anions (orange) and two equivalents of cyanostar (grey, Figure 1B), as sketched in Figure 1. [44][45] The SMILES concept has been demonstrated for a range of prevalent dye classes in both thin films and crystals 44 as well as in nanoparticles, [46][47] yielding both very high brightness and high dye density in the solids (up to ~0.5 M, or one dye per 3.5 nm 3 ).…”