Fluorescent carboxylic and phosphonic acids: comparative photophysics from solution to organic nanoparticles

Abstract

Phosphonic and carboxylic fluorescent nanoparticles have been fabricated by direct reprecipitation in water. Their fluorescence properties strongly differ from those of the corresponding esters where strong H-bonding formation is prohibited. Comparative experiments between the two acid derivatives, differing only in their acid functions while keeping the same alkyl chain, have evidenced the peculiar behavior of the phosphonic acid derivative compared to its carboxylic analog. A dramatic emission quenching for the phosphonic acid in aprotic toluene could be observed while a fivefold increase in the fluorescence signal was observed for molecules assembled as nanoparticles. Such properties have been attributed on the theoretical basis to the formation of folded conformers in solution, leading to deactivation of the radiative excited state through intramolecular H-bonding. These studies evidence for the first time through time-resolved fluorescence measurements the stronger H-donating character of phosphonic acids compared to the carboxylic ones, and provide information on the degree of structural heterogeneity within the nanoparticles. They should pave the way for the rational fabrication of chelating acid fluorophores, able to complex metal oxides to yield stiff hybrid magnetofluorescent nanoparticles which are attracting considerable attention in the growing fields of bimodal imaging and vectorization applications.

Boron Difluoride Curcuminoid Fluorophores with Enhanced Two‐Photon Excited Fluorescence Emission and Versatile Living‐Cell Imaging Properties

“…As depicted in Figure S34 in the Supporting Information, the Cos7 cells became fluorescently labeled upon exposure to particles of compounds 3 ‐BF 2 , and 4 ‐BF 2 . Because these aggregates are non‐fluorescent and have sizes that are as big as those of the cells, we attributed the fluorescence enhancement to the penetration of compounds 3 ‐BF 2 and 4 ‐BF 2 as non‐aggregated species due to a disaggregation mechanism at the cell membrane . However, the spectra of the dyes within the cells resemble those obtained in the apolar dibutyl ether solvent with an emission in the visible region ( λ em =629 nm, Figure S35 in the Supporting Information).…”

“…These results by using pre‐formed particles of compounds 3 ‐BF 2 and 4 ‐BF 2 show that the particles are disrupted at the cell membrane, leading to the uptake of non‐aggregated dye molecules . As such, we present a means of cell labeling with molecular fluorophores that are not water soluble.…”

Strong Color Tuning of Self‐Assembled Azo‐Derived Phosphonic Acids upon Hydrogen Bonding

“…These studies demonstrate that phosphonic acid units clearly act as H‐bond donor groups as already proposed for another kind of photoactive compound, incorporating a fluorescent moiety and a phosphonic acid unit. In that case, H‐bonding intramolecular interactions between both the phosphonic unit and an H‐accepting group of the fluorophore was permitted by a flexible ethylenoxy linker and reported to cause dramatic emission quenching in solution …”

“…ChemPhotoChem 2017, 1,6-11 www.chemphotochem.org noxy linker and reported to cause dramatic emission quenching in solution. [27] Following the H-bond donatinga bility of AzoHBP,w ea nticipated dramatic influence of the solvent proticity and Lewis basicity on the azo capability for E-Z photoisomerization.I ndeed, photoisomerization performed under excitation at4 88 nm was effective only in aprotics olvents with as trong b value like THF and DMF, and reached am inimum conversion yield 1 min of 47 %a nd 52 %, respectively (TableS2). Conversely,p hotoisomerization was fully inhibited in protic solvents like methanol or in chlorinateds olvents where aggregation seemed to occur on the basis of UV/Vis absorption studies.…”

Are Fluorescent Organic Nanoparticles Relevant Tools for Tracking Cancer Cells or Macrophages?

“…[ 2a , 17 ] We ascribed this remarkable emissive properties to the apolar surroundings of each chromophore brought by the alkyl chains and destabilizing the polar excited state that would relax otherwise in a few picoseconds upon internal conversion. [ 18 ] The structural confi nement of the molecules within a single nanoparticle causes restricted mobility, limiting the probability of radiationless deactivation and leading in some cases to novel π−π aggregation-induced emissive nanomaterials. [ 19 ] Such π−π interactions are excluded here as mentioned previously.…”