Boranils: Versatile Multifunctional Organic Fluorophores for Innovative Applications

Julien Massue,Gilles Ulrich,Denis Jacquemin

doi:10.3390/org2040020

Abstract

Multifunctional stimuli-responsive fluorophores showing bright environment-sensitive emissions have fueled intense research due to their innovative applications in the fields of biotechnologies, optoelectronics, and materials. A strong structural diversity is observed among molecular materials, which has been enriched over the years with a growing responsiveness to stimuli. Boron dipyrromethene (BODIPY) dyes have long been the flagship of emissive boron complexes due to their outstanding properties until a decade ago when analogues based on N^O, N^N, or N^C π-conjugated chelates emerged. The finality of developing borate dyes was to compensate for BODIPYs’ lack of solid-state fluorescence and small Stokes shifts while keeping their excellent optical properties in solution. Among them, the borate complexes based on a salicylaldimine ligand, called by the acronym boranils appear as the most promising, owing to their facile synthesis and dual-state emission properties. Boranil dyes have proven to be good alternatives to BODIPY dyes and have been applied in applications such as bioimaging, bioconjugation, and detection of biosubstrates. Meanwhile, ab initio calculations have rationalized experimental results and provided insightful feedback for future designs. This review article aims at providing a concise yet representative overview of the chemistry around the boranil core with the subsequent applications.

Highlights

The current research aiming to engineer new fluorescent dyes is highly dynamic and primarily arises from fruitful collaborations between chemists, physicists, and biologists, continuously fueled by the applications of molecular probes in many fields, e.g., biomedical imaging, analysis, sensing, detection, materials science, etc
Scientific innovation has led to major developments in the field of organic electronics including organic light-emitting diodes (OLED), photovoltaic cells, solar energy concentrators, or transistors [1,2,3]
One of the most popular families of organic dyes in recent decades is undoubtedly constituted of 4,4 -difluoro-4-bora-3a,4a-diaza-s-indacene derivatives, known as Boron dipyrromethene (BODIPY) dyes [15,16,17,18]

Summary

Introduction

The current research aiming to engineer new fluorescent dyes is highly dynamic and primarily arises from fruitful collaborations between chemists, physicists, and biologists, continuously fueled by the applications of molecular probes in many fields, e.g., biomedical imaging, analysis, sensing, detection, materials science, etc. Synthetic efforts notably allowed fine-tuning of the emission color, up to the near infra-red (NIR) and replacement of the fluoro ligands on boron by functionalized A wide panel of boranils structures has been reported over the years, with a strong emphasis on fine-tuning the emission color over the whole visible range, while maintaining a strong emission intensity both in solution and in the solidstate [31,32,33,34,35,36,37].

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