# Regioselective Synthesis of Ambipolar B–N Lewis Pair Functionalized Pyrenes: Structural Dynamics, Emission Tuning, and Applications in Live Cell Imaging and as Electrochemiluminescent Materials

## TL;DR

This paper describes the synthesis of new pyrene-based molecules with tunable optical properties for use in live cell imaging and electrochemiluminescent materials.

## Contribution

The study introduces a novel method for creating ambipolar B–N Lewis pair functionalized pyrenes with enhanced optical and electrochemical properties.

## Key findings

- The synthesized pyrenes show intense fluorescence with quantum yields up to 82% and red-shifted emission.
- The molecule 5-Pf effectively stains acidic compartments in live cells and performs well as an electrochemiluminescent material.
- 5-Pf achieved an ECL efficiency of 0.9 ± 0.1%, surpassing that of [Ru(bpy)3]2+.

## Abstract

Intramolecular B←N Lewis pair functionalization
of polycyclic
aromatic hydrocarbons (PAHs) is emerging as a powerful strategy for
tailoring their optical and electronic properties to specific applications.
Herein, we report the design and synthesis of four quadrupolar pyrene
fluorophores containing triarylamine donor and pyridyl-borane acceptor
substituents by N-directed electrophilic C–H borylation in
the K-region. Introduction of rigid six-membered B–N heterocycles
greatly decreased the lowest unoccupied molecular orbital (LUMO) energy
levels and red-shifted the absorption and emission maxima compared
to the nonborylated precursors. These pyrenes exhibit absorptions
spanning the entire visible region and intense green to deep red and
near-infrared fluorescence, with impressive quantum yields as high
as 82%. The simultaneous presence of pyridyl-borane acceptor and arylamine
donor units also enables facile reversible multiredox oxidation and
reduction processes. The advantageous photophysical and electrochemical
characteristics are highly attractive for optoelectronic devices and
(bio)­imaging applications. The pyrene derivative with the most red-shifted
emission, 5-Pf, was further evaluated in live cell imaging
studies, showing effective staining of acidic compartments, including
lysosomes. In addition, we demonstrate the outstanding performance
of 5-Pf as a novel electrochemiluminescent (ECL) luminophore
through annihilation and coreactant experiments in cyclic voltammetry
and pulsing modes. Spooling ECL spectroscopy revealed a strong emission
with a maximum at 646 nm, in good agreement with the photoinduced
emission maximum at 660 nm. A superior absolute ECL efficiency (ΦECL) of up to 0.9 ± 0.1%, exceeding that of typically
employed [Ru­(bpy)3]2+, was achieved during CV
scanning with benzoyl peroxide as a coreactant.