Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 27, Issue 47, Pages 12144-12155Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202101264
Keywords
cyclic voltammetry; electroluminescence; naphthalene diimides; scanning probe microscopy; tripodal platforms
Categories
Funding
- Helmholtz Research Program STN (Science and Technology of Nanosystems)
- DFG [MA 2605/6-1]
- DAAD [57299294]
- 111 Project [90002-18011002]
- Projekt DEAL
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The study found that adding pyrrolidinyl group can enhance the fluorescence of NDI chromophores and cause a significant redshift in their absorption spectrum, resulting in a narrower bandgap. By using cyclic voltammetry, it was revealed that the redox properties of NDIs are influenced by core substituents, and the adsorption behavior of NDIs on a gold surface was observed.
This paper reports the efficient synthesis, absorption and emission spectra, and the electrochemical properties of a series of 2,6-disubstituted naphthalene-1,4,5,8-tetracarboxdiimide (NDI) tripodal molecules with thioacetate anchors for their surface investigations. Our studies showed that, in particular, the pyrrolidinyl group with its strong electron-donating properties enhanced the fluorescence of such core-substituted NDI chromophores and caused a significant bathochromic shift in the absorption spectrum with a correspondingly narrowed bandgap of 1.94 eV. Cyclic voltammetry showed the redox properties of NDIs to be influenced by core substituents. The strong electron-donating character of pyrrolidine substituents results in rather high HOMO and LUMO levels of -5.31 and -3.37 eV when compared with the parental unsubstituted NDI. UHV-STM measurements of a sub-monolayer of the rigid tripodal NDI chromophores spray deposited on Au(111) show that these molecules mainly tend to adsorb flat in a pairwise fashion on the surface and form unordered films. However, the STML experiments also revealed a few molecular clusters, which might consist of upright oriented molecules protruding from the molecular island and show electroluminescence photon spectra with high electroluminescence yields of up to 6x10(-3). These results demonstrate the promising potential of the NDI tripodal chromophores for the fabrication of molecular devices profiting from optical features of the molecular layer.
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