Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril.

Mohammad A Alnajjar,Knut Rurack,Mohamed Nilam,Andreas Hennig,Pichandi Ashokkumar,Werner M Nau,Jürgen Bartelmeß,Robert Hein

doi:10.3762/bjoc.14.171

Abstract

We introduce herein boron-dipyrromethene (BODIPY) dyes as a new class of fluorophores for the design of reporter dyes for supramolecular host–guest complex formation with cucurbit[7]uril (CB7). The BODIPYs contain a protonatable aniline nitrogen in the meso-position of the BODIPY chromophore, which was functionalized with known binding motifs for CB7. The unprotonated dyes show low fluorescence due to photoinduced electron transfer (PET), whereas the protonated dyes are highly fluorescent. Encapsulation of the binding motif inside CB7 positions the aniline nitrogen at the carbonyl rim of CB7, which affects the pKa value, and leads to a host-induced protonation and thus to a fluorescence increase. The possibility to tune binding affinities and pKa values is demonstrated and it is shown that, in combination with the beneficial photophysical properties of BODIPYs, several new applications of host–dye reporter pairs can be implemented. This includes indicator displacement assays with favourable absorption and emission wavelengths in the visible spectral region, fluorescence correlation spectroscopy, and noncovalent surface functionalization with fluorophores.

Highlights

We report the synthesis and photophysical characterization of BODIPY derivatives with an aniline substituent in the meso-position to which different anchor groups have been attached, and we investigate their complexation behaviour with CB7
Cucurbit[n]urils (CBn, n = 5–8, 10, and 14) are a class of macrocyclic host molecules which are water soluble, nontoxic, and are able to bind a large variety of neutral and cationic guests in their inner cavity with high affinity [1,2,3,4]
For the preparation of the aminomethyladamantane derivative 5, a route via a bromophenylBODIPY BDP-Br followed by a Buchwald–Hartwig coupling was performed

Summary

Introduction

We report the synthesis and photophysical characterization of BODIPY derivatives with an aniline substituent in the meso-position to which different anchor groups have been attached, and we investigate their complexation behaviour with CB7. The goal was to explore the suitability of this approach, the possibility to fine-tune binding constants with different anchor groups and to provide BODIPYs with different absorption and emission wavelengths as well as pKa values of the aniline substituent.

Results

Conclusion