New 2,6‐Distyryl‐Substituted BODIPY Isomers: Synthesis, Photophysical Properties, and Theoretical Calculations

Abstract

A 2,6-distyryl-substituted boradiazaindacene (BODIPY) dye and a new series of 2,6-p-dimethylaminostyrene isomers containing both α- and β-position styryl substituents were synthesized by reacting styrene and p-dimethylaminostyrene with an electron-rich diiodo-BODIPY. The dyes were characterized by X-ray crystallography and NMR spectroscopy and their photophysical properties were investigated and analyzed by carrying out a series of theoretical calculations. The absorption spectra contain markedly redshifted absorbance bands due to conjugation between the styryl moieties and the main BODIPY fluorophore. Very low fluorescence quantum yields and significant Stokes shifts are observed for 2,6-distyryl-substituted BODIPYs, relative to analogous 3,5-distyryl- and 1,7-distyryl-substituted BODIPYs. Although the fluorescence of the compound with β-position styryl substituents on both pyrrole moieties and one with both β- and α-position substituents was completely quenched, the compound with only α-position substituents exhibits weak emission in polar solvents, but moderately intense emission with a quantum yield of 0.49 in hexane. Protonation studies have demonstrated that these 2,6-p-dimethylaminostyrene isomers can be used as sensors for changes in pH. Theoretical calculations provide strong evidence that styryl rotation and the formation of non-emissive charge-separated S1 states play a pivotal role in shaping the fluorescence properties of these dyes. Molecular orbital theory is used as a conceptual framework to describe the electronic structures of the BODIPY core and an analysis of the angular nodal patterns provides a reasonable explanation for why the introduction of substituents at different positions on the BODIPY core has markedly differing effects.

Rational Engineering of BODIPY‐Bridged Trisindole Derivatives for Solar Cell Applications

“…Shen et al almost simultaneously demonstrated that the 2,6-distyryl Bodipy could be synthesized through a Heck reaction using a 2,6-diiodo-Bodipy derivative. [10] However, when using an electron-rich p-dimethylaminostyryl building-block, the authors observed systematically the creation of three isomers with styryl substituents being connected either to the ß-or α-positions. Due to such uncontrolled isomerisation leading only to 9% of isolated yield of the targeted ß-position isomer, this Heck-approach has not been retained either.…”

“…Actually, vinyl groups at 2,6 positions have been reported very recently, but only with methyl groups at 3,5 positions. [9,10] Bröring et al…”

“…BODIPY dyes with vinyl groups at 2a nd 6p ositions were reported very recently,b ut only with methylg roups at the 3a nd 5p ositions. [9,10] Brçringa nd co-workerss ynthesized aB ODIPY dimer, composed of two BODIPYc ores linked together at the b positions by av inyl bond, by using am ethatetic homodimerization approach. [9] Unfortunately,d imerization of the 1,3,5,7-tetramethyl hindered BODIPY core following metathesis reaction optimization with the highly active Grubbs II catalyst could only be achieved with al ow yield (17 %).…”

A 3,5‐DistyrylBODIPY Dye Functionalized with Boronic Acid Groups for Direct Electrochemical Glucose Sensing

“…Styrylation is a convenient means to red-shift the main spectral band of BODIPY dyes on this basis [39,40]. The p-conjugation system of BODIPY dyes can be extended by structurally modifying the 3,5-positions of the BODIPY core in this manner.…”

Functionalization of 3,5,8-Trichlorinated BODIPY Dyes

“…Halogenated BODIPYs are particularly versatile substrates for functionalization purposes via both cross-coupling and nucleophilic substitution reactions, and all halogens (fluoride, chloride, bromide, and iodide) have been introduced into the pyrrolic positions of BODIPY (or a dipyrromethane or pyrrole precursor), mainly using electrophilic substitution. 5,6,22−26 In particular, functionalization of the BODIPY core at the 3,5-positions significantly affects the spectroscopic and photophysical properties, and this strategy has been exploited for the synthesis of a variety of functionalized BODIPYs, from 3,5-dichloro- or 3,5-diiodo-BODIPY precursors. 13,14,17−21 On the other hand, a very useful method for facile transformation of dipyrroketones into 5-chlorodipyrromethene salts using phosgene was developed by Fischer and Orth 27 and has since been exploited by others 28,29 and ourselves.…”