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Density-Matrix Approach for the Electroluminescence of Molecules in a Scanning Tunneling Microscope
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0002-3915-300X
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0003-0007-0394
2011 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 106, no 17, 177401- p.Article in journal (Refereed) Published
Abstract [en]

The electroluminescence (EL) of molecules confined inside a nanocavity in the scanning tunneling microscope possesses many intriguing but unexplained features. We present here a general theoretical approach based on the density-matrix formalism to describe the EL from molecules near a metal surface induced by both electron tunneling and localized surface plasmon excitations simultaneously. It reveals the underlying physical mechanism for the external bias dependent EL. The important role played by the localized surface plasmon on the EL is highlighted. Calculations for porphyrin derivatives have reproduced corresponding experimental spectra and nicely explained the observed unusual large variation of emission spectral profiles. This general theoretical approach can find many applications in the design of molecular electronic and photonic devices.

Place, publisher, year, edition, pages
2011. Vol. 106, no 17, 177401- p.
Keyword [en]
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-33953DOI: 10.1103/PhysRevLett.106.177401ISI: 000290098200005ScopusID: 2-s2.0-79960647801OAI: diva2:421624
QC 20110609Available from: 2011-06-09 Created: 2011-05-23 Last updated: 2013-05-20Bibliographically approved
In thesis
1. Electron-vibration coupling and its effects on optical and electronic properties of single molecules
Open this publication in new window or tab >>Electron-vibration coupling and its effects on optical and electronic properties of single molecules
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis is devoted to theoretical investigations of electron-vibration coupling and its effects on optical and electronic properties of single molecules, especially for molecules confined between metallic electrodes.

A density-matrix approach has been developed to describe the photon emission of single molecules confined in the scanning tunneling microscope (STM). With this new method electronic excitations induced by both the tunneling electron and the localized surface plasmon (LSP) can be treated on an equal footing. Model calculations for porphyrin derivatives have successfully reproduced and explained the experimentally observed unusual variation of the photon emission spectra. The method has also been extended to study the STM induced fluorescence and phosphorescence of C60 molecules in combination with the first principles calculations. In particularly, the non-Condon vibronic couplings have been exclusively included in the calculations. The experimental spectra have been nicely reproduced by our calculations, which also enable us to identify the unique spectral fingerprint and origin of the measured spectra. The observed rich spectral features have been finally correctly assigned.

The electron transport properties of molecular junctions with bipyridine isomers have been studied in the sequential tunneling (SET) regime by assuming that the molecules are weakly coupled to metallic electrodes. It is shown that the strong electron-vibration coupling in the 2, 2’-bipyridine molecule and the 4,4’-bipyridine molecule can lead to observable Franck-Condon blockade. Taking advantage of such novel effect, a gate-controlled conductance switch with ideal on-off ratio has been proposed for a molecular junction with the 4, 4’-bipyridine molecule.

The effect of the electron-vibration coupling on one-photon and two-photon absorption spectra of green fluorescent protein (GFP) has been systematically examined. The hydroxybenzylidene-2, 3-dimethylimidazolinone molecule in the deprotonated anion state (HBDI) is used to model the fluorescence chromophore of the GFP. Both Condon and non-Condon vibronic couplings have been considered in the calculations. The calculated spectra are in good agreement with the available experimental spectra. It confirms the notion that the observed blue-shift of the two-photon absorption spectrum with respect to its one-photon absorption counterpart is caused by the non-Condon vibronic coupling.

All the calculations are carried out with our own software package, DynaVib. It is capable of modeling a variety of vibrational-resolved spectroscopies, such as absorption, emission, and resonant Raman scattering (RRS) spectra. In our package, the Duschinsky rotation and non-Condon effect have been fully taken into account. Both time-independent and time-dependent approaches have been implemented, allowing to simulate the spectra of very large molecules.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xiv, 66 p.
Trita-BIO-Report, ISSN 1654-2312 ; 2013:10
National Category
Theoretical Chemistry
urn:nbn:se:kth:diva-122180 (URN)978-91-7501-773-0 (ISBN)
Public defence
2013-06-07, FA32, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 14:00 (English)

QC 20130520

Available from: 2013-05-20 Created: 2013-05-14 Last updated: 2013-05-20Bibliographically approved

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