Extended BODIPYs as Red-NIR Laser Radiation Sources with Emission from 610 nm to 750 nm.

Herein, we report the synthetic access to a set of π-extended BODIPYs featuring a penta-arylated (phenyl and/or thiophene) dipyrrin framework. We take advantage of the full chemoselective control of 8-methylthio-2,3,5,6-tetrabromoBODIPY when we conduct the Liebeskind-Srogl cross-coupling (LSCC) to functionalize exclusively the meso-position, followed by the tetra-Suzuki reaction to arylate the halogenated sites. All these laser dyes display absorption and emission bands in the red edge of the visible spectrum reaching the near-infrared with thiophene functionalization. The emission efficiency, both fluorescence and laser, of the polyphenylBODIPYs can be enhanced upon decoration of the peripheral phenyls with electron donor/acceptor groups at para positions. Alternatively, the polythiopheneBODIPYs show an astonishing laser performance despite the charge transfer character of the emitting state. Therefore, these BODIPYs are suitable as a palette of stable and bright laser sources covering the spectral region from 610 nm to 750 nm.

Structure and Conformation of Novel BODIPY Ugi Adducts.

Two novel BODIPY-Ugi (boron dipyrromethene) adducts exhibit peculiar room temperature (T=20 °C) H-1 NMR spectra in that several protons located at the aromatic aniline-type ring are lost in the baseline. This observation revealed the existence of a dynamic conformational process where rotation around the C-N bond is hindered. Variable-temperature H-1 and C-13 NMR spectroscopic analysis confirmed this conclusion; that is, low-temperature spectra show distinct signals for all four aromatic protons below coalescence, whereas average signals are recorded above coalescence (T=+120 °C). Particularly interesting was the rather large difference in chemical shifts for the ortho protons below coalescence, Δδ=1.45 ppm, which was explained based on DFT computational analysis. Indeed, the calculated lowest-energy gas-phase conformation of the BODIPY Ugi adducts locates one half of the aniline-type ring in the shielding anisotropic cone of the bridge phenyl ring in the BODIPY segment. This is in contrast to the solid-state conformation established by X-ray diffraction analysis that shows a nearly parallel arrangement of the aromatic rings, probably induced by crystal packing forces.

BODIPY as electron withdrawing group for the activation of double bonds in asymmetric cycloaddition reactions.

In this work we have found that a BODIPY can be used as an electron withdrawing group for the activation of double bonds in asymmetric catalysis. The synthesis of cyclohexyl derivatives containing a BODIPY unit can easily be achieved via trienamine catalysis. This allows a new different asymmetric synthesis of BODIPY derivatives and opens the door to future transformation of this useful fluorophore. In addition, the Quantum Chemistry calculations and mechanistic studies provide insights into the role of BODIPY as an EWG.

Synthesis, Photophysical Study, and Biological Application Analysis of Complex Borondipyrromethene Dyes.

A series of complex boronic acids were prepared through multicomponent reactions (MCRs). Both Passerini and Ugi MCRs were carried out in which one component was an arylboronic acid. The resulting highly functionalized boronic acids participated efficiently in the Liebeskind-Srogl cross-coupling reaction with meso-methylthioBODIPY derivatives to yield complex borondipyrromethene (BODIPY) dyes in good yields. The joined spectroscopic and computational study points out the deep impact of the arylated chromophoric position on the photophysical signatures. Thus, unconstrained aryls grafted at the meso position did not sway the spectral band positions but switched on new nonradiative relaxation channels, whereas additional arylation at the opposite α-pyrrolic position softened such fluorescence quenching and shifted the emission to the red-edge of the visible spectrum. The conducted biological analysis revealed that peripheral blood mononuclear cells incubated with these new compounds showed reduced cytotoxicity and retained their normal activities. Additionally, the dyes remained stable inside the cells after 24 h of incubation. These results demonstrated that these novel fluorescent probes based on BODIPY can be applied for cell imaging and analysis, expanding their applications.

Exploring viscosity, polarity and temperature sensitivity of BODIPY-based molecular rotors.

Microviscosity is a key parameter controlling the rate of diffusion and reactions on the microscale. One of the most convenient tools for measuring microviscosity is by fluorescent viscosity sensors termed 'molecular rotors'. BODIPY-based molecular rotors in particular proved extremely useful in combination with fluorescence lifetime imaging microscopy, for providing quantitative viscosity maps of living cells as well as measuring dynamic changes in viscosity over time. In this work, we investigate several new BODIPY-based molecular rotors with the aim of improving on the current viscosity sensing capabilities and understanding how the structure of the fluorophore is related to its function. We demonstrate that due to subtle structural changes, BODIPY-based molecular rotors may become sensitive to temperature and polarity of their environment, as well as to viscosity, and provide a photophysical model explaining the nature of this sensitivity. Our data suggests that a thorough understanding of the photophysics of any new molecular rotor, in environments of different viscosity, temperature and polarity, is a must before moving on to applications in viscosity sensing.

FormylBODIPYs: Privileged Building Blocks for Multicomponent Reactions. The Case of the Passerini Reaction.

Eleven formyl-containing BODIPY dyes were prepared by means of either the Liebeskind-Srogl cross-coupling reaction or the Vilsmeier reaction. These dyes were used as components in the Passerini reaction to give highly substituted BODIPY dyes. A joined spectroscopic and theoretical characterization of the synthesized compounds was conducted to unravel the impact of the structural rigidity/flexibility on the photophysical signatures. These dyes were tested as fluorescent trackers for phagocytosis. Additionally, they proved to be useful to stain different blood cells with an intense and stable signal at a very low exposure time.