Photophysical Properties of Boron-Derived Fluorophores

Boron-derived fluorophores encompass a diverse family of compounds in which a boron centre is incorporated into conjugated organic frameworks to yield bright, stable emitters. Prominent examples include boron-dipyrromethene (BODIPY) and its aza- and fluoro-substituted analogues, alongside bis(difluoroboron) complexes of pyrroles (BOPHY). These dyes combine strong absorption in the visible or near-infrared region with high fluorescence quantum yields, narrow emission bands and tunable Stokes shifts. Key photophysical parameters—absorption/emission maxima, quantum yield, excited-state lifetime and environmental sensitivity—are modulated by ligand design, substituent pattern and supramolecular interactions. Mechanisms such as intramolecular charge transfer and twisted intermolecular charge transfer govern large Stokes shifts and dual emission, while rigidified scaffolds suppress non-radiative decay. Owing to their photostability, ease of functionalisation and spectral tunability, boron fluorophores find application in biological imaging, sensing of analytes, photocatalysis and light-harvesting assemblies.

Research from Nature Portfolio

Recent studies have elucidated new design strategies for boron complexes that exploit donor–acceptor architectures and nanoparticle formulations. One investigation synthesised unsymmetrical pyridine-pyrazolate ligands bearing boron(III) centres to promote strong intramolecular charge transfer. The resulting complexes exhibit mega Stokes shifts of up to 263 nm, dual emission arising from locally excited and twisted charge-transfer states, and extended excited-state lifetimes relative to classical BODIPY dyes, rendering them promising for long-lifetime sensing. Another report describes boron-based photosensitiser nanoparticles engineered for simultaneous ratiometric fluorescence imaging and photodynamic therapy. Upon reaction with over-expressed polyamines in cancer cells, these pyrrolopyrrole-aza BODIPY-derived particles generate enhanced phototoxic species and permit real-time tracking of intracellular analyte levels, marrying efficient fluorescence reporting with targeted therapeutic action.

Photophysical Properties of Boron-Derived Fluorophores publication trend

The graph below shows the total number of articles in photophysical properties of boron-derived fluorophores across all publications each year (not limited to Nature Index journals).

Technical terms

Stokes shift: Difference between the peak wavelengths of absorption and emission, indicating energy loss upon relaxation.

Quantum yield: Ratio of the number of photons emitted to those absorbed, reflecting fluorescence efficiency.

Intermolecular charge transfer (ICT): Electronic transition in which an excited electron moves from a donor moiety to an acceptor within the same molecule.

Excited-state lifetime: Average duration a molecule remains in an excited state before returning to the ground state via photon emission or non-radiative processes.

Ratiometric fluorescence imaging: Analytical technique using intensity ratios at two emission wavelengths to quantify changes in analyte concentration or environment.

References

1. Characterization of nanoparticles combining polyamine detection with photodynamic therapy. Communications Biology (2021).
2. Synthesis and photophysical investigations of pyridine-pyrazolate bound boron(III) diaryl complexes. Scientific Reports (2022).
3. Facile Synthesis of Asymmetric aza-Boron Dipyrromethene Analogues Bearing Quinoxaline Moiety. Molecules (2023).
4. Hybridising inorganic materials with fluorescent BOPHY dyes: A structural and optical comparative study. Frontiers in Chemistry (2022).