Ultrafast Aggregation-Induced Tunable Emission Enhancement in a Benzothiadiazole-Based Fluorescent Metal–Organic Framework Linker
AuthorsGutierrez Arzaluz, Luis
Mohammed, Omar F.
KAUST DepartmentAdvanced Membranes and Porous Materials (AMPM) Center, Physical Sciences and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
Advanced Membranes and Porous Materials Research Center
Chemical Science Program
Functional Materials Design, Discovery and Development (FMD3)
KAUST Solar Center (KSC)
Physical Science and Engineering (PSE) Division
Ultrafast Laser Spectroscopy and Four-dimensional Electron Imaging Research Group
KAUST Grant NumberCARF-FCC/1/1972-63-01
Embargo End Date2022-11-30
Permanent link to this recordhttp://hdl.handle.net/10754/673874
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AbstractAggregation-induced emission enhancement (AIEE) is a process recently exploited in solid-state materials and organic luminophores, and it is explained by tight-molecular packaging. However, solution-phase AIEE and its formation mechanism have not been widely explored. This work investigated AIEE phenomena in two donor–acceptor–donor-type benzodiazole-based molecules (the organic building block in metal–organic frameworks) with an acetylene and phenyl π-conjugated backbone tapered with a carboxylic acid group at either end. This was done using time-resolved electronic and vibrational spectroscopy in conjunction with time-dependent density functional theory (TD-DFT) calculations. Fluorescence up-conversion spectroscopy and time-correlated single-photon counting conclusively showed an intramolecular charge transfer-driven aggregate emission enhancement. This is shown by a red spectral shift of the emission spectra as well as an increase in the fluorescence lifetime from 746 ps at 1.0 × 10–11 to 2.48 ns at 2.0 × 10–3 M. The TD-DFT calculations showed that a restricted intramolecular rotation mechanism is responsible for the enhanced emission. The femtosecond infrared (IR) transient absorption results directly revealed the structural dynamics of aggregate formation, as evident from the evolution of the C≡C vibrational marker mode of the acetylene unit upon photoexcitation. Moreover, the IR data clearly indicated that the aggregation process occurred over a time scale of 10 ps, which is consistent with the fluorescence up-conversion results. Interestingly, time-resolved results and DFT calculations clearly demonstrated that both acetylene bonds and the sulfur atom are the key requirements to achieve such a controllable aggregation-induced fluorescence enhancement. The finding of the work not only shows how slight changes in the chemical structure of fluorescent chromophores could make a tremendous change in their optical behavior but also prompts a surge of research into a profound understanding of the mechanistic origins of this phenomenon. This may lead to the discovery of new chemical strategies that aim to synthesize novel chromophores with excellent optical properties for light-harvesting applications.
CitationGutiérrez-Arzaluz, L., Nadinov, I., Healing, G., Czaban-Jóźwiak, J., Jia, J., Huang, Z., … Mohammed, O. F. (2021). Ultrafast Aggregation-Induced Tunable Emission Enhancement in a Benzothiadiazole-Based Fluorescent Metal–Organic Framework Linker. The Journal of Physical Chemistry B. doi:10.1021/acs.jpcb.1c08889
SponsorsThe authors thank the King Abdullah University of Science and Technology (KAUST) and the CARF-FCC/1/1972-63-01 project for financial support and the Supercomputing Laboratory at KAUST for computational and storage resources.
PublisherAmerican Chemical Society (ACS)