Organoboron Polymorphs with Different Molecular Packing Modes for Optical Waveguides.

Area of Science:

• Materials Science
• Organic Chemistry
• Optoelectronics

Background:

• Organoboron compounds are emerging as promising candidates for designing optoelectronic materials due to their tunable electronic properties and high fluorescence efficiency.
• Developing materials with narrowband emission and high photoluminescence quantum yield (PLQY) is crucial for advanced optical applications.

Purpose of the Study:

• To synthesize a novel organoboron compound, B-BNBP, with a double B←N bridged bipyridine core and four fluorine atoms.
• To investigate the controllable preparation of its polymorphic crystals and explore their structure-property relationships.
• To evaluate the optoelectronic properties, including emission spectra, PLQY, and optical waveguide performance.

Main Methods:

• Facile synthesis of the organoboron compound B-BNBP.
• Controllable preparation of polymorphic crystals via solution self-assembly methods.
• Crystallographic analysis and theoretical calculations to understand molecular packing and intermolecular interactions.
• Photoluminescence spectroscopy to characterize emission properties.
• Optical loss measurements for waveguide performance evaluation.

Main Results:

• The synthesized B-BNBP compound exhibits a narrowband emission spectrum and a high PLQY of 86.53% in solution.
• Two distinct polymorphic microcrystals, 1D-microstrips (1D-MSs) and 2D-microdisks (2D-MDs), were prepared, showing H-aggregation and J-aggregation, respectively.
• Strong emission with a full width at half maximum (FWHM) < 30 nm was observed in thin films and 2D-MDs.
• 1D-MSs demonstrated thermally activated delayed fluorescence (TADF) and superior optical waveguide performance with an optical loss of 0.061 dB/μm.

Conclusions:

• The study successfully synthesized a novel organoboron compound with excellent fluorescence properties.
• Controllable polymorphism and distinct aggregation behaviors (H- and J-aggregation) were achieved, influencing optical properties.
• The findings highlight the potential of organoboron micro/nano-crystals for advanced optoelectronic devices, particularly in optical waveguides, and reveal critical structure-property relationships.