Dipyrrolylquinoxaline difluoroborates with intense red solid-state fluorescence.

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Organic fluorescent dyes are crucial for various applications, including organic light-emitting diodes (OLEDs) and sensors.
• Developing novel fluorescent materials with enhanced solid-state emission properties is an active area of research.
• Dipyrrolylquinoxalines (PQs) and their BF2 complexes (BPQs) represent a class of organic compounds with potential for unique photophysical properties.

Purpose of the Study:

• To synthesize and characterize a series of dipyrrolylquinoxaline (PQ) and BF2 complex (BPQ) organic fluorescent dyes.
• To investigate the optical and electrochemical properties of these novel dyes in solution and solid states.
• To elucidate the structure-property relationships governing their fluorescence behavior, particularly in the solid state.

Main Methods:

• Synthesis of PQ and BPQ dyes from commercial reagents.
• Characterization using X-ray structural analysis.
• Optical spectroscopy (absorption and fluorescence) to determine spectral properties and quantum yields.
• Electrochemical measurements to assess redox potentials.
• Analysis of crystal packing structures to understand intermolecular interactions.

Main Results:

• BPQs displayed intense, broad absorption in the visible region, with absorption maxima red-shifted by over 110 nm compared to PQs (up to 583 nm).
• Most synthesized dyes exhibited red solid-state fluorescence with moderate to high quantum yields, while one PQ showed bright yellow fluorescence.
• X-ray structures revealed planar quinoxaline cores with BF2 chelation and near-perpendicular pyrrole orientation, indicating extended π-conjugation.
• Well-ordered intermolecular packing via hydrogen bonding was observed, with a lack of π-π stacking, potentially explaining the strong solid-state fluorescence.

Conclusions:

• The synthesized dipyrrolylquinoxaline (PQ) and BF2 complex (BPQ) dyes possess significant potential as solid-state emitters.
• Extended π-conjugation and specific intermolecular interactions, such as hydrogen bonding, are key factors in achieving intense solid-state fluorescence.
• These findings contribute to the design of novel organic fluorescent materials with tunable optical properties for advanced applications.