Highly Fluorescent Dianionic Polymethines with a 1,3,2-Dioxaborine Core

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Difluoroboron β-diketonate motifs are increasingly utilized in synthesizing polymethine fluorophores.
• Polymethine dyes are crucial for applications spanning the visible and near-infrared (NIR) spectral regions.

Purpose of the Study:

• To synthesize and characterize a new series of dianionic cyanine dyes with a central dioxaborine ring.
• To investigate the spectral properties, including absorption and fluorescence, of these novel dyes with varying electron-acceptor terminal groups.

Main Methods:

• Synthesis of A¹-π-A-π-A¹ type dianionic cyanine dyes incorporating a central dioxaborine ring (A).
• Spectroscopic analysis (absorption and fluorescence) to determine photophysical properties.
• Evaluation of solvatochromism and quantum yields in various solvents.

Main Results:

• Intensive absorption bands (molar extinction up to 380,000 M^-1 cm^-1) were observed in the 530-770 nm range, tunable by terminal groups.
• Absorption and fluorescence spectra showed near mirror-image symmetry with minimal solvatochromism, except in methanol.
• High fluorescence quantum yields were achieved, up to 92% in the visible range and 18-37% for NIR dyes in DMF.

Conclusions:

• The synthesized dianionic cyanine dyes offer tunable photophysical properties for visible and NIR applications.
• The difluoroboron β-diketonate core enables the creation of highly emissive and stable fluorophores.
• These dyes represent promising candidates for advanced optical and imaging technologies.