Efficient Upper-Excited State Fluorescence in an Organic Hyperbolic Metamaterial.
basic_science · Level V
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- Record sourced from PubMed, PMID 29470077.
- Also identified by DOI 10.1021/acs.nanolett.7b04738.
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Abstract
Upper-excited state emission is not usually observed from molecules owing to competition with much faster nonradiative relaxation pathways; however, it can be made more efficient by modifying the photonic density of states to enhance the radiative decay rate. Here, we show that embedding the small molecule zinc tetraphenylporphyrin (ZnTPP) in a hyperbolic metamaterial enables an ∼18-fold increase in fluorescence intensity from the second singlet excited state ( S<sub>2</sub>) relative to that from the lowest singlet excited state ( S<sub>1</sub>). By varying the number of periods in the HMM stack, we are able to systematically tune the ZnTPP fluorescence spectrum from red (dominated by emission from S<sub>1</sub>) to blue (dominated by emission from S<sub>2</sub>) with an instrument-limited decay lifetime <10 ps. Our results are consistent with a broadband Purcell enhancement in the radiative rate of both transitions predicted via transfer matrix modeling and point to a general opportunity to harness upper-excited states for spectrally tunable, ultrafast fluorescence via radiative decay engineering.