Vibrationally Resolved Fluorescence Excited with Submolecular Precision

Qiu, X. H.; Nazin, George V.; Ho, W.

doi:10.1126/science.1078675

Cited by 574 publications

(630 citation statements)

References 32 publications

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“…[10][11][12][13][14][15] The enormous potential of porphyrins for the fabrication of tailor-made functional molecular architectures on well-defined substrates has stimulated significant activities in fundamental research. 4,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] In this contribution, we review recent advances in the understanding of the dynamic behaviour of porphyrins, as representatives of organic molecules, adsorbed on a Cu(111) single crystal surface in ultra-high vacuum (UHV). Based on temperaturedependent measurements of individual molecules, the kinetics and energetics of diffusion 33,34 and rotation, 34 of the so-called self-metalation reaction 35,36 and finally of conformational switching of particular free base porphyrins 37 can be determined.…”

Section: Introductionmentioning

confidence: 99%

Studying the dynamic behaviour of porphyrins as prototype functional molecules by scanning tunnelling microscopy close to room temperature

Marbach

Steinrück

2014

Chem. Commun.

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Scanning tunnelling microscopy (STM) enables us to directly observe the dynamic behaviour of organic molecules on surfaces. While imaging atoms and molecules using STM is certainly fascinating by itself, corresponding temperature-dependent measurements allow for the quantitative determination of the energetics and kinetics of the underlying molecular surface processes. Herein, we review recent advances in the STM investigation of the dynamic behaviour of adsorbed porphyrins at and close to room temperature.Three different case studies are discussed, providing insight into the dynamics of diffusion, rotation, reaction, and molecular switching at surfaces, based on isothermal STM measurements. The reviewed examples demonstrate that variable temperature STM can be a suitable tool to directly monitor the dynamic behaviour of individual adsorbed molecules, at and close to room temperature. Free base porphyrins on Cu(111) proved to be particularly suitable for these studies due to the strong bonding interaction between the iminic nitrogen atoms in the porphyrin macrocycle and the Cu substrate atoms. As a consequence, the corresponding activation energies for surface diffusion, self-metalation reaction and conformational switching are of a magnitude that allows for monitoring the processes at and around room temperature, in contrast to most previous studies, which were performed at cryogenic temperatures. The kinetic analysis of the surface diffusion and self-metalation was performed using an Arrhenius approach, yielding the corresponding activation energies and preexponential factors. In contrast, the conformational switching process was analysed in the framework of transition state theory, based on the Eyring equation. This approach provides a more detailed insight into interpretable thermodynamic potentials, i.e., the enthalpic and entropic contributions to the activation barrier. The analysis shows that at room temperature the adsorption and switching behaviour of the investigated free base porphyrin on Cu(111) is dominated by entropic effects. Since the entropic energy contribution vanishes at low temperatures, the importance of experiments conducted at temperatures close to room temperature is emphasized.

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Section: Introductionmentioning

confidence: 99%

Studying the dynamic behaviour of porphyrins as prototype functional molecules by scanning tunnelling microscopy close to room temperature

Marbach

Steinrück

2014

Chem. Commun.

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“…Ultrathin metal oxide layers have been used to reduce the electronic interaction between molecules and substrates allowing the observation of fluorescence [4], vibronic states [5], and charging of isolated molecules [6]. Franke et al have recently reduced the electronic coupling of C 60 with a metal surface by locking and lifting each fullerene with a second molecular species [7].…”

Section: Introductionmentioning

confidence: 99%

Stabilization of bimolecular islands on ultrathin NaCl films by a vicinal substrate

et al. 2009

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a b s t r a c tThe structure of ultrathin NaCl films on Au(1 1 1) and on Au(11 12 12), as well as the one of bimolecular 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) and 1,4-bis-(2,4-diamino-1,3,5,-triazine)-benzene (BDATB) islands on NaCl films on both surfaces have been studied with a low-temperature scanning tunnelling microscope. We show that intermixed bimolecular assemblies based on selective three-fold hydrogen-bonding (H-bonding), that have previously been observed on Au(1 1 1) and on Au(11 12 12), can also be stabilized on insulating NaCl films on Au, however, only if these films are grown on Au(11 12 12) and not on Au(1 1 1). The behaviour of the heterocomplex structures is found to be largely influenced by the structural properties of the underlying substrate and by the number of NaCl layers. On a partly NaCl-covered Au(1 1 1) surface, the excess of molecules after completion of the first layer on Au prefers to form a second molecular layer based on ordered heterocomplex structures rather than to adsorb on the NaCl islands. The use of a vicinal surface together with the strong cohesion characteristic of the NaCl film introduces smooth elastic deformations on the NaCl(0 0 1) plane. As a consequence, the periodically modified structure of the overlayer provides preferential binding sites and allows adsorption of two-dimensional molecular structures. In contrast to what is observed on Au(11 12 12), the molecular domains on the NaCl film do not follow the Au step directions, but the NaCl(0 0 1) high symmetry directions. Our results provide a strategy to increase the adsorption energy of flat molecules on insulating layers by choosing a vicinal metal substrate.

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“…We focus on the regime of sequential tunneling relevant to STM experiments on passivated surfaces [29]. We present a fully analytical treatment of the quantum yield within a generic model system.…”

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confidence: 99%