Excited state dynamics of BODIPY-based acceptor-donor-acceptor systems: a combined experimental and computational...

Area of Science:

• Photophysics and photochemistry
• Materials science
• Supramolecular chemistry

Background:

• Donor-bridge-acceptor (D-π-A) systems, particularly those incorporating boron dipyrromethene (BODIPY), are promising for bio-imaging and sensing due to their sensitivity to environmental factors.
• Understanding the structure-photophysical property relationship is crucial for optimizing molecular sensor performance.

Purpose of the Study:

• Investigate the excited-state dynamics of novel acceptor-donor-acceptor (A-D-A) molecules featuring benzodithiophene and BODIPY units.
• Elucidate the influence of solvent polarity on the photophysical behavior and excited-state evolution of these A-D-A systems.

Main Methods:

• Ultrafast spectroscopy was employed to probe transient absorption spectra.
• Density Functional Theory (DFT)-based electronic structure calculations were utilized to complement experimental findings.

Main Results:

• Photoexcitation of A-D-A molecules generated an initial excited species with a near-infrared absorption band, irrespective of solvent polarity.
• Subsequent excited-state dynamics were highly dependent on solvent polarity, leading to different charge transfer states in non-polar (toluene) versus polar (tetrahydrofuran) solvents.
• Structural relaxation and charge delocalization were observed in non-polar solvents, while polar solvents promoted fully charge-separated states.

Conclusions:

• Solvent polarity significantly dictates the excited-state pathways and charge separation characteristics of BODIPY-based A-D-A systems.
• Molecular design parameters, including donor-acceptor distance and steric hindrance, can be manipulated to tune excited-state photophysics for targeted applications in sensing and bio-imaging.