UV—vis spectroscopy of the coupling products of the palladium-catalyzed C—H arylation of the BODIPY core

Abstract

The steady-state, UV-vis electronic absorption and fluorescence emission properties of a large set of 3-aryl and 3,5-diaryl substituted difluoroboron dipyrromethene dyes obtained via direct, palladiumcatalyzed C-H (het)arylation of the BODIPY core are reported. The spectra display the narrow absorption and fluorescence emission bands and the generally quite small Stokes shifts characteristic of classic difluoroboron dipyrrins. As a function of the solvent, the spectral maxima are located within a very narrow wavelength range and are slightly red-shifted with increasing solvent polarizability, which is shown to be the crucial parameter influencing the wavelength position of the maxima. The extended π-conjugation in the 3,5-diaryl products always leads to bathochromically shifted absorption and emission spectra compared to those of the 3-aryl analogues. The derivative with a 3-mesityl substituent has blue-shifted spectra in comparison to its 3-phenyl substituted analogue, reflecting the diminished π-conjugation in the former due to steric strain. The nature of the meso-aryl has only a small effect on the spectral positions but affects the fluorescence quantum yield Φ. The majority of the dyes have high Φ (>0.85), except the compounds with meso-phenyl and meso-( p-nitrophenyl) substituents. Quantumchemical calculations were performed to evaluate the differences in spectroscopic properties upon substitution of the BODIPY core and to compare them with the corresponding experimental results.

Novel Alkoxy‐Substituted Dipyrrins and Near‐IR BODIPY Dyes—Preparation and Photophysical Properties

“…The absorptions and emissions of BODIPYs 12 – 19 are listed in Table . It includes the values of BODIPY 20 without methoxy groups as a benchmark dye and the tetrathien‐2‐yl‐substituted BODIPY 21 for comparison. Figure depicts the photographs of solutions of meso ‐pentafluorophenyl‐substituted compounds 15 , 16 , and 17 in methanol and their UV/Vis and fluorescence spectra.…”

“…[a] Recorded at c =10 −5 mol L −1 in 1‐cm cuvettes; [b] After excitation at λ max (absorption); [c] Values taken from ref. ; [d] Measurements in dichloromethane as reported in ref. .…”

Postfunctionalization of the BODIPY Core: Synthesis and Spectroscopy

“…The extended π‐conjugation of the 3,5‐diaryl products 85 is shown in the red‐shifted absorption and fluorescence emission spectra in relation to those of the 3‐substituted analogues 84 . The nature of the meso ‐aryl system has only a small effect on the spectral positions but affects the Φ values 89…”

Radical CH Arylation of the BODIPY Core with Aryldiazonium Salts: Synthesis of Highly Fluorescent Red‐Shifted Dyes

“…[4] Most derivation strategies for synthesizing new boron dipyrrins either start from suitably functionalized pyrroles [5] or use reactive BODIPY dyes [6,7] (Scheme 1). However,these two methodologies tend to suffer from the use of unstable intermediates and/or the need for al ong synthetic route.A more efficient method of introducing functional groups is by C À Hfunctionalization reactions, [8,9] allowing the synthesis of new dyes in asingle atom economical step.Afew examples of such direct derivatization reactions for these fluorophores are currently known, [10,11] most of which require rather forcing reaction conditions to overcome the inertness of the CÀH bond which limits the scope and the obtained yield.…”

“…These results demonstrate the vast improvement of the present radical CÀHarylation compared to previous arylation protocols. [5,11] This new method provides easy access to new compounds in amuch shorter reaction time,because most of these radical reactions are completed within one hour. Furthermore,o ur new procedure supplies compounds in ah igher yield in one atom-economical step avoiding the use of multistep synthesis,h igh reaction temperatures,a nd unstable pyrrole intermediates.…”