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Exploring Differences in Excited-State Properties of Styryl-BODIPY Chromophores upon Change from α- to β-Substitution.
- Source :
- Zeitschrift für Physikalische Chemie; Dec2020, Vol. 234 Issue 12, p1735-1758, 24p
- Publication Year :
- 2020
-
Abstract
- We present a femtosecond pump-probe UV-Vis broadband transient absorption spectroscopy study of two styryl-substituted BODIPY chromophores with different position of the substituent. The α-substituted isomer shows typical BODIPY-type spectral features, such as sharp absorption and emission bands, a small Stokes shift and an excited-state lifetime in the 4 ns range, which only weakly depends on the solvent. In contrast, β-styryl-BODIPY features much broader steady-state absorption and emission spectra and a larger Stokes shift, particularly in polar solvents. Transient absorption spectroscopy including a complete global kinetic analysis reports a substantial decrease in S<subscript>1</subscript> lifetime to 300 ps for polar solvents upon change from α- to β-substitution. In the case of the α-isomer, TD-DFT calculations identify a typical "cyanine-type" electron rearrangement upon S<subscript>0</subscript> → S<subscript>1</subscript> excitation accompanied by a slight reduction in dipole moment. In contrast, the same transition in the β-isomer shows strong intramolecular charge transfer (ICT) character involving a substantial increase in dipole moment. Assuming a simple energy-gap-law argument, the accelerated nonradiative decay of the β-isomer in polar solvents may be linked to the decrease of the S<subscript>1</subscript>(ICT)-S<subscript>0</subscript> energy difference. BODIPY dyes with a conjugated substituent in β-position therefore suffer a substantial loss in fluorescence brightness in polar environments compared with their α-substituted counterparts. This might limit their applicability in fluorescence imaging. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 09429352
- Volume :
- 234
- Issue :
- 12
- Database :
- Complementary Index
- Journal :
- Zeitschrift für Physikalische Chemie
- Publication Type :
- Academic Journal
- Accession number :
- 148382114
- Full Text :
- https://doi.org/10.1515/zpch-2019-1374