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

• Published in: Physical chemistry chemical physics : PCCP Vol. 23; no. 14; pp. 89 - 897
• Main Authors: Wei, Zimu, Sharma, Sushil, Philip, Abbey M, Sengupta, Sanchita, Grozema, Ferdinand C
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 14.04.2021
• Subjects: Absorption spectra; Charge transfer; Electronic structure; Excitation; Near infrared radiation; Optimization; Photoexcitation; Solvents; Spectrum analysis; Steric hindrance; Tetrahydrofuran; Toluene
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp00453k

Donor-bridge-acceptor systems based on boron dipyrromethene (BODIPY) are attractive candidates for bio-imagining and sensing applications because of their sensitivity to temperature, micro-viscosity and solvent polarity. The optimization of the properties of such molecular sensors requires a detailed knowledge of the relation between the structure and the photophysical behavior in different environments. In this work we have investigated the excited-state dynamics of three acceptor-donor-acceptor molecules based on benzodithiophene and BODIPY in solvents of different polarities using a combination of ultrafast spectroscopy and DFT-based electronic structure calculations. Transient absorption spectra show that upon photoexcitation an initial excited species with an induced absorption band in the near-infrared regime is formed independent of the solvent polarity. The subsequent photophysical processes strongly depend on the solvent polarity. In non-polar toluene this initial excited state undergoes a structural relaxation leading to a delocalized state with partial charge transfer character, while in the more polar tetrahydrofuran a fully charge separated state is formed. The results clearly show how factors such as donor-acceptor distance and restricted rotational motion by steric hindrance can be used to tune the excited state photophysics to optimize such systems for specific applications. Donor-bridge-acceptor systems based on boron dipyrromethene (BODIPY) are attractive candidates for bio-imagining and sensing applications because of their sensitivity to temperature, micro-viscosity and solvent polarity.