Borondifluoride complexes of hemicurcuminoids as bio-inspired push–pull dyes for bioimaging

Abstract

Hemicurcuminoids are based on half of the π-conjugated backbone of curcuminoids. The synthesis of a series of such systems and their borondifluoride complexes is described. The electrochemical and photophysical properties of difluorodioxaborine species were investigated as a function of the nature of electron donor and acceptor groups appended at either terminal positions of the molecular backbone. The emissive character of these dipolar dyes was attributed to an intraligand charge transfer process, leading to fluorescence emission that is strongly dependent on solvent polarity. Quasi-quantitative quenching of fluorescence in high polarity solvents was attributed to photoinduced electron transfer. These dyes were shown to behave as versatile fluorophores. Indeed, they display efficient two-photon excited fluorescence emission leading to high two-photon brightness values. Furthermore, they form nanoparticles in water whose fluorescence emission quantum yield is less than that of the dye in solution, owing to aggregation-induced fluorescence quenching. When cos7 living cells were exposed to these weakly-emitting nanoparticles, one- and two-photon excited fluorescence spectra showed a strong emission within the cytoplasm that originated from the individual molecules. Dye uptake thus involved a disaggregation mechanism at the cell membrane which restored fluorescence emission. This off-on fluorescence switching allows a selective optical monitoring of those molecules that do enter the cell, which offers improved sensitivity and selectivity of detection for bioimaging purposes.

Exciton Interactions, Excimer Formation, and [2π+2π] Photodimerization in Nonconjugated Curcuminoid‐BF2 Dimers

“…This indicates that one curcuminoid C−C double bond is no longer present in the photoproduct while the other one is left unreacted, which is consistent with the UV/Vis spectrum of the photoproduct showing an absorption band at ca. 395 nm similar to that recorded for a hemicurcuminoid derivative . The phenyl proton resonances are split, which further indicates desymmetrization of the curcuminoid backbone.…”

“…395 nm similar to that recorded for ah emicurcuminoid derivative. [25] The phenyl protonr esonancesa re split, which further indicates desymmetrization of the curcuminoid backbone. Importantly, new resonance peaks are found at higher field at ca.…”

Electric-field induced bistability in single-molecule conductance measurements for boron coordinated curcuminoid compounds

“…On the other hand, the affinity of curcumin for boron is well known to provide coloured materials such as rosocyanine, used for detection of trace amounts of boron in various media 30. CCMs require CCM-boron intermediates toward their synthesis25 and there are examples in the literature, such as the CRANAD derivatives, that are used as sensors in the near-IR area, mainly for Alzheimer's disease studies 31…”

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

“…Spectroscopic measurements and X‐ray structure determinations were performed according to published methodologies . Compounds 1 ‐H, 1 ‐BF 2 , 2 ‐H, 6 ‐H, 5 ‐BF 2 , 8 ‐BF 2 , M 1 ‐H, M 6 ‐H, M 1 ‐BF 2 , and M 6 ‐BF 2 were synthesized following published procedures.…”