Polybrominated BOPHY Dyes: Synthesis, Reactivity, and Properties

Abstract

A series of mono- to hexabrominated BOPHY dyes have been regioselectively synthesized in 41-96% yields from bromination of parent bis(difluoroboron)-1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine (BOPHY), bromination of hydrazine-linked bispyrrole intermediate, or brominated 2-formylpyrrole precursors in moderate to excellent yields. The reactivities of these polybrominated BOPHY dyes were further studied via regioselective nucleophilic substitution or Suzuki/Stille cross-coupling reactions from which a series of 5- or 5,5'-substituted BOPHYs with amine, pyrrole, thiophene, and phenyl groups were obtained in moderate to high yields of 37-94%. The regioselectivities of both the bromination and nucleophilic substitution reaction, and these resultant BOPHY dyes, are confirmed by NMR, HRMS, and crystal structures. The spectroscopic properties of these resultant BOPHYs were studied, and most of them showed strong absorbance and bright fluorescence with maximum wavelengths centered at between the range of 430 and 660 nm. Their absorption and emission spectra were red-shifted for each bromine atom incorporated. The positions in which bromines or substituents are attached modulate the photophysical properties of the resulting BOPHY dyes.

Investigations on the Synthesis, Reactivity, and Properties of Perfluoro‐α‐Benzo‐Fused BOPHY Fluorophores

“…BOPHY 10 is the first di‐substituted dipyrrolyl‐BOPHY reported, with the most bathochromically shifted absorption and emission of this type of compound. This is in agreement with previous investigations of pyrrolyl‐based substituents at the 3,5‐positions of BODIPY or 3‐position of BOPHY, as an effective method to shift their absorption and emission wavelengths to the near‐IR region [7a,19] …”

“…Treatment of BOPHY 1 with 10 equivalents of bromine in chloroform [7a,19] led to the formation of 3,8‐dibrominated BOPHY 2 in 72 % yield, as shown in Scheme 1. BOPHY 2 was recrystallized from dichloromethane/methanol and directly used in reactivity studies, as shown in Schemes 2 and 3.…”

“…To explore the reactivity of the dibromo‐dodecafluoro‐BOPHY fluorophore, Pd(0)‐catalyzed coupling reactions and aromatic nucleophilic substitution reactions (S N Ar) with O‐, C‐, N‐, S‐nucleophiles were carried out to modify the 3,8‐positions via the bromine handle [7a] . As we have previously reported, [18] the Suzuki and Stille cross‐coupling reactions tend to afford higher yields of functionalized products compared with other coupling reactions, such as Sonogashira and Heck, due to their milder reaction conditions.…”

Synthesis, Photophysics and Redox Properties of Aza‐BODIPY Dyes with Electron‐Donating Groups

“…A significant increase of the fluorescence for the diprotonated species [aza‐BODIPY+2H + ], in comparison with the weakly fluorescent monoprotonated form [aza‐BODIPY+H + ] and the nearly non‐emissive neutral 6 , is associated with the inhibition of the intramolecular charge transfer (ICT). These preliminary results indicate that compounds presented in this paper could operate as a novel potential “turn‐on” pH sensors where protonation of the NMe 2 groups alleviates ICT and increases the fluorescence quantum yield (φ fl ) …”

A Beneficial Effect of Bromination on the Photophysical and Photochemical Properties of Aza‐BODIPY Dyes with Electron‐Donating Groups

“…Compounds 5 to 8 , due to the presence of dimethylamino groups (Me 2 N‐), proved to be sensitive to the pH value . Exemplarily, toluene solution of aza‐BODIPY 6 upon titration with trifluoroacetic acid (TFA, Figure ) showed a stepwise disappearance of the absorption band at λ abs 675 nm with the concomitant evolution of a blue‐shifted absorption band at λ abs 660 nm, meaning formation of a fully protonated form of 6 , viz.…”