Ultrafast Energy Transfer Determines the Formation of Fluorescence in DOM and Humic Substances.
Environ Sci Technol
; 55(15): 10365-10377, 2021 08 03.
Article
em En
| MEDLINE
| ID: mdl-34260209
ABSTRACT
Humification is a ubiquitous natural process of biomass degradation that creates multicomponent systems of nonliving organic matter, including dissolved organic matter (DOM) and humic substances (HS) in water environments, soils, and organic rocks. Despite significant differences in molecular composition, the optical properties of DOM and HS are remarkably similar, and the reason for this remains largely unknown. Here, we employed fluorescence spectroscopy with (sub)picosecond resolution to elucidate the role of electronic interactions within DOM and HS. We revealed an ultrafast decay component with a characteristic decay lifetime of 0.5-1.5 ps and spectral diffusion originating from excitation energy transfer (EET) in the system. The rate of EET was positively correlated to the fraction of aromatic species and tightness of aromatic species packing. Diminishing the number of EET donor-acceptor pairs by reduction with NaBH4 (decrease of the acceptor number), decrease of pH (decrease of the electron-donating ability), or decrease of the average particle size by filtration (less donor-acceptor pairs within a particle) resulted in a lower impact of the ultrafast component on fluorescence decay. Our results uncover the role of electronic coupling among fluorophores in the formation of DOM and HS optical properties and provide a framework for studying photophysical processes in heterogeneous systems of natural fluorophores.
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Substâncias Húmicas
Idioma:
En
Revista:
Environ Sci Technol
Ano de publicação:
2021
Tipo de documento:
Article
País de afiliação:
Federação Russa