Intense Circularly Polarized Luminescence Induced by Chiral Supramolecular Assembly: The Importance of Intermolecular Electronic Coupling.

Herein we report on circularly polarized luminescence (CPL) emission originating from supramolecular chirality of organic microcrystals with a |glum| value up to 0.11. The microcrystals were prepared from highly emissive difluoroboron ß-diketonate (BF2dbk) dyes R-1 or S-1 with chiral binaphthol (BINOL) skeletons. R-1 and S-1 exhibit undetectable CPL signals in solution but manifest intense CPL emission in their chiral microcrystals. The chiral superstructures induced by BINOL skeletons were confirmed by XRD analysis. Spectral analysis and theoretical calculations indicate that intermolecular electronic coupling, mediated by the asymmetric stacking in the chiral superstructures, effectively alters excited-state electronic structures and facilitates electron transitions perpendicular to BF2bdk planes. The coupling increases cosθµ,m from 0.05 (monomer) to 0.86 (tetramer) and triggers intense optical activity of BF2bdk. The results demonstrate that optical activity of chromophores within assemblies can be regulated by both orientation and extent of intermolecular electronic couplings.

Pure Organic Room Temperature Phosphorescence from Excited Dimers in Self-Assembled Nanoparticles under Visible and Near-Infrared Irradiation in Water.

Pure organic room temperature phosphorescence (RTP) has unique advantages and various potential applications. However, it is challengeable to achieve organic RTP under visible and near-infrared (NIR)-light excitation, especially in aqueous solution. Herein we assemble difluoroboron ß-diketonate compounds to form organic nanoparticles (NPs) in water. The resulting NPs are able to show efficient RTP, effective uptake, and bright imaging of HeLa cells under both visible- and NIR-light excitation. More strikingly, spectroscopic study, single-crystal X-ray diffraction, and DFT calculation reveal that the efficient RTP in organic NPs is originated from dimers in their excited states. The multiple interactions and intermolecular charge transfer in the dimer structures are of significance in promoting the production of dimer triplet excited states and suppressing the nonradiative decays to boost the RTP under visible- and NIR-light irradiation in water.

Synthesis of N,O,B-Chelated Dipyrromethenes through an Unexpected Intramolecular Cyclisation: Enhanced Near-Infrared Emission in the Aggregate/Solid State.

The first example of the synthesis of mono-N,O-B-chelated dipyrromethene (BODIPY) derivatives through an unexpected intramolecular nucleophilic displacement of the fluorine by alkenols in the presence of boron trifluoride as Lewis acid is reported. The chlorine in the indacene core allowed for further structural modifications through nucleophilic substitutions or palladium-catalysed coupling reactions to afford new fluorophores with tuneable photophysical properties. Their expanded conjugation structure resulted in distinct red-shifted absorption and emission spectra in organic solutions. Furthermore, the twisted steric hindrance of the benzene substitution patterns suppressed aggregation-induced quenching, leading to an enhanced NIR emission in the aggregate/solid state, which was rarely observed for BODIPY dyes. Nanoparticles of the fluorophores formed by the assembly with the polymeric surfactant F127 were successfully used for bioimaging of living cells and for tumour-targeted imaging in a tumour-bearing mouse model.

A Simple Strategy to Construct Amorphous Metal-Free Room Temperature Phosphorescent and Multi-Color Materials.

It is urgent to develop a universal strategy for producing small organic molecules exhibiting efficient room temperature phosphorescence (RTP). An important contribution made by Ma and Tian et al. provides a general and applicable strategy to obtain amorphous organic molecules with efficient RTP emission by simply modifying phosphors onto ß-cyclodextrin (ß-CD). The nonradiative decay processes and oxygen quenching have been significantly suppressed by the strong intermolecular hydrogen bonding between ß-CD derivatives. Furthermore, the cavity of ß-CDs endows them with the ability to incorporate the adamantane moiety of the fluorescent guest molecules to construct a supramolecular system which exhibits excellent RTP-fluorescence dual emission properties and multicolor emission by altering the host to guest ratio and the excitation wavelength.

Light-Harvesting Systems Based on Organic Nanocrystals To Mimic Chlorosomes.

We report the first highly efficient artificial light-harvesting systems based on nanocrystals of difluoroboron chromophores to mimic the chlorosomes, one of the most efficient light-harvesting systems found in green photosynthetic bacteria. Uniform nanocrystals with controlled donor/acceptor ratios were prepared by simple coassembly of the donors and acceptors in water. The light-harvesting system funneled the excitation energy collected by a thousand donor chromophores to a single acceptor. The well-defined spatial organization of individual chromophores in the nanocrystals enabled an energy transfer efficiency of 95 %, even at a donor/acceptor ratio as high as 1000:1, and a significant fluorescence of the acceptor was observed up to donor/acceptor ratios of 200 000:1.

Ratiometric O2 sensing based on selective self-sensitized photooxidation of donor-acceptor fluorophores.

We report a series of organic fluorophores that undergo selective self-sensitized photooxidation upon light irradiation in air accompanied by a change of fluorescence from yellow to blue on the seconds timescale. The distinct emission changes allow the ratiometric quantitation of O2 concentration.

Water-soluble, membrane-permeable organic fluorescent nanoparticles with large tunability in emission wavelengths and Stokes shifts.

Entrapment within surface-crosslinked micelles (SCMs) enhanced the emission of conventional hydrophobic fluorescent dyes, endowed them with excellent water solubility and membrane permeability, and greatly expanded the Stokes shifts without any covalent structural modification of the dyes.