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Probing the electronic state of a single coronene molecule by the emission from proximate fluorophores.

Authors
Type
Published Article
Journal
ChemPhysChem
1439-7641
Publisher
Wiley Blackwell (John Wiley & Sons)
Publication Date
Volume
13
Issue
4
Pages
938–945
Identifiers
DOI: 10.1002/cphc.201100785
PMID: 22253201
Source
Medline
License
Unknown

Abstract

We measured electronic transitions of the 2D graphene-type molecule hexa-peri-hexabenzocoronene (HBC) at the single-molecule level. The large intersystem crossing rate and long triplet state lifetime in the range of seconds are prohibitive for direct single-molecule observation. By covalently coupling fluorescent acceptor molecules (perylenecarboximide, PMI) to HBC, efficient singlet energy transfer gives rise to strong PMI fluorescence. Confocal single-molecule fluorescence microscopy with two excitation colours matching the HBC and PMI transition frequencies, respectively, was conducted. Single HBC-6PMI molecules were readily observed via the PMI emission. It was found that after selective excitation of the HBC the PMI emission is interrupted by dark intervals whose length of several seconds is in agreement with the triplet state lifetime of HBC. Accordingly, the presence/absence of PMI emission permits to read out the spin state of a single HBC molecule. Moreover, due to spectral overlap, the HBC triplet state acts as an energy acceptor for PMI in the excited singlet state, thus leading to efficient singlet-triplet annihilation (STA) during its lifetime. Hence, intersystem crossing into the HBC triplet state serves as a collective fluorescence switch for individual multichromophores.

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