Spectroscopy of BODIPY in solid phase: crystal and nanoparticles

Area of Science:

• Photophysics and spectroscopy
• Materials science
• Organic electronics

Background:

• Frenkel exciton theory describes excited-state coupling in molecular crystals.
• BODIPY dyes are fluorescent organic compounds with diverse applications.
• Understanding solid-state properties is crucial for material design.

Purpose of the Study:

• To compare experimental spectra of adamantyl mesityl BODIPY single crystals and nanoparticles with Frenkel theory predictions.
• To investigate the influence of solid-state structure on optical properties.
• To determine the structural nature (crystalline vs. amorphous) of BODIPY nanoparticles.

Main Methods:

• Synthesis of adamantyl mesityl BODIPY.
• Single crystal X-ray crystallography.
• Measurement of birefringence, dichroism, and refractive indices.
• Absorption and fluorescence spectroscopy.
• Application of Frenkel exciton theory and TDDFT calculations.
• Nanoparticle synthesis using 3D hydrodynamic focusing microfluidics.

Main Results:

• Single crystals displayed monoclinic structure with transition moments in a common plane.
• Refractive index difference (Δn) of 0.11 was measured.
• Experimental absorption spectrum of the monocrystal was accurately reproduced by Frenkel theory without adjustable parameters.
• Nanoparticles exhibited molecule-like absorption, reproduced by Frenkel model with strong disorder.
• Optical leaks in the spectrophotometer were identified and accounted for.

Conclusions:

• Frenkel exciton theory successfully predicts the optical properties of adamantyl mesityl BODIPY single crystals.
• Synthesized nanoparticles are concluded to be amorphous due to strong disorder observed in their spectra.
• The study highlights the importance of structural characterization for understanding photophysical properties.