Adsorption‐induced changes of intramolecular optical transitions:<scp>PTCDA</scp>/NaCl and PTCDA/KCl

Hochheim, Manuel; Bredow, Thomas

doi:10.1002/jcc.23990

Cited by 13 publications

(42 citation statements)

References 58 publications

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“…Consequently, they attributed E gas-dilute solely to the polarization of the alkali-metal halide substrate assuming a vanishing polarizability of He (identical to vacuum). However, recent DFT calculations came to a different conclusion, namely that PTCDA is bent markedly due to the bonding with the NaCl(100) surface [72][73][74]. The authors of Ref.…”

Section: Comparison With Ptcda On Nacl(100) and Kcl(100)mentioning

confidence: 99%

“…The authors of Ref. [74] computed the absorption energies for the gas-phase molecule and for an isolated molecule on the alkali-metal halide surface which, according to them, differ by 114 meV (for the 6-311G * basis set), of which E dist = 26 meV are caused by molecular distortion and E elec = 36 meV by electrostatic interaction between PTCDA and NaCl. While these numbers depend on the employed basis set, they demonstrate nonetheless that more factors contribute significantly to the measured shift E gas-dilute than merely the substrate polarizability.…”

Section: Comparison With Ptcda On Nacl(100) and Kcl(100)mentioning

confidence: 99%

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Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

et al. 2016

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The optical excitation energies of organic dye molecules are often said to depend sensitively on the polarizability of the utilized substrate. To this end, we employ differential reflectance spectroscopy (DRS) to analyze the S 0 → S 1 fundamental transition energies observed for 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) as a function of coverage on various surfaces, such as sp 2-bonded insulating layers [graphene and hexagonal boron nitride (h-BN)], and noble metals pre-covered by a molecular wetting layer which prevents hybridization of the second-layer molecules with the metal states. We elucidate the optical absorbance behavior of PTCDA layers grown on h-BN/Rh(111) and on h-BN/Pt(111) and characterize their structures by means of scanning tunneling microscopy. Surprisingly, although the dielectric properties of the employed substrates differ substantially, only two main transition energies are observed: (i) PTCDA HE essentially mimics the behavior of isolated monomers on surfaces (particularly at submonolayer coverage), while (ii) PTCDA LE , red-shifted by ≈ 70 meV (≈ 560 cm −1), is attributed to two-dimensional densely packed aggregates. This red-shift is in remarkable accordance with previous investigations for PTCDA on NaCl(100) and, therefore, likely arises from the same physical effects, namely the formation of two-dimensional excitonic bands and the polarizability of neighboring molecules within the monolayer. In distinction from earlier studies, we conclude that the polarizabilities of the employed substrates do not constitute the dominant contribution to the molecular S 0 → S 1 transition energies observed here.

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Section: Comparison With Ptcda On Nacl(100) and Kcl(100)mentioning

confidence: 99%

Section: Comparison With Ptcda On Nacl(100) and Kcl(100)mentioning

confidence: 99%

Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

et al. 2016

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“…On KCl, PTCDA forms a commensurate brickwall structure [112]. DFT calculations [113] have shown that a single PTCDA molecule on a KCl or NaCl terrace prefers an adsorption site in which the perylene backbone is positioned above a Cl − anion at a distance of 2.72 Å and 2.54 Å, respectively, while the oxygens atoms are located close to the cations in the surface. This leads to a distortion of the molecule similar to the situation on Ag (100) and Ag (110) but with an even more pronounced downward shift of the carboxylic oxygen atoms.…”

Section: Bonding Of Ptcda On Inorganic Surfacesmentioning

confidence: 99%

Long Vertical Distance Bonding of the Hexagonal Boron Nitride Monolayer on the Cu(111) Surface

et al. 2017

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viii Cu(111)-Substrat auf. Stärkere Wechselwirkungen an der Grenzfläche wurden nur dann gefunden, wenn die hBN-Schicht eine höhere Dichte an strukturellen Defekten aufwies. In diesen Fällen konnte die darunter liegende Cu(111)-Oberfläche die azimutale Orientierung der PTCDA-Domänen beeinflussen. Abschließend wurden die optischen Eigenschaften von PTCDA/hBN/Cu(111) gemessen und mit denen von PTCDA/Cu(111), wo die erste PTCDA-Lage die höheren PTCDA-Lagen von der Metalloberfläche entkoppelt, verglichen. Raman-Linien wurden für beide Systeme gemessen und mit denen von PTCDA auf anderen Substraten verglichen. Auf beiden Substraten, hBN/Cu(111) und Cu(111), wurde Fluoreszenz gemessen von Molekülen, die an Oberflächendefekten adsorbiert sind, und von Molekülen in höheren Lagen (ab der zweiten Lage auf hBN/Cu(111) und ab der dritten Lage auf Cu(111)). Die Fluoreszenz lag bei ˜18.450 cm −1 bzw. ˜18.150 cm −1 . Nur auf hBN/Cu(111) wurde Fluoreszenz von geordneten Molekülen in der ersten Lage bei ˜18.300 cm −1 gemessen. Allerdings ist die Fluoreszenzintensität von PTCDA auf hBN/Cu(111) klein und die Lebenszeiten der angeregten Zustände liegt bei nur (1, 6 − 4, 4) • 10 −14 s. Diese Untersuchungen zeigten, dass eine einzelne hBN-Schicht nur zu einem gewissen Grad in der Lage ist, das PTCDA-Molekül von einer Cu(111)-Oberfläche zu entkoppeln. Einerseits ähnelt das PTCDA-Molekül auf hBN/Cu(111) PTCDA-Molekülen in der Gasphase stärker als solchen, die auf einer Metalloberfläche adsorbiert sind. Andererseits wird das PTCDA-Molekül durch die hBN-Schicht nicht ausreichend entkoppelt, um eine Auslöschung einer elektronischen Anregung zu verhindern. Trotz einer Reduktion der Ladungsübertragung zwischen den Schichten sind die Fluoreszenz-Intensitäten und die Quantenausbeute gering.

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“…This observation is consistent with the results by Müller et al on PTCDA adsorbed on KCl thin films on Ag(100) [58] who reported that the vibrational modes of the adsorbed molecule are very similar to those of the free molecule, but due to the presence of the substrate additional low energy modes couple to the transition. This was further confirmed by DFT calculations where the redshift of the first optical excitation was found to stem from both the distortion of the molecule due to the interaction with the surface and the electrostatic potential of the surface play an important role [110].…”

Section: B Influence Of Coulomb Interactionsmentioning

confidence: 55%

Stereoisomeric selection upon adsorption: A structural and optical study of curcuminoid derivatives on ultrathin films of KCl on Au(111) and on bulk KCl(001)

et al. 2021

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We present a combined Scanning Tunneling Microscopy (STM), non-contact Atomic Force Microscopy (nc-AFM) and Differential Reflectance Spectroscopy (DRS) study aiming at the characterization of the relationship between structural and optical properties of a supramolecular assembly of a curcuminoid derivative adsorbed on two kinds of substrates: bilayers of KCl on Au (111) (2 ML KCl/Au(111)) and KCl(001) bulk. The molecule features a difluoroboron (-BF 2 ) complex as well as cyano (-CN) end groups, which induces an internal dipole moment of a few Debyes. The comparative study of the structural properties of the molecules adsorbed on 2 ML KCl/Au(111), which allows for STM characterization, and KCl bulk, which allows for nc-AFM and DRS characterization, shows that the molecular adsorption is similar on both substrates. STM and nc-AFM give evidence that the on-surface condensation of the molecules into supramolecular assemblies is steered by two main interactions: the molecule-substrate interaction between the -CN end groups of the molecule and the cationic K + species, as well as an in-plane intermolecular interaction involving -BF 2 and phenyl groups. Based on Density Functional Theory calculations, we propose an epitaxial molecular structure described by a two-molecules unit cell forming a 8 × 2 supercell on the KCl surface that grows in form of ribbons along the < 100 > or < 010 > directions of the substrate, which are polar. Among several possible stereo-isomers for the molecule, it is found that the balance between vertical and in-plane interactions selects the one whose size matches the distance between K + species to condense on the substrate and not the most stable one stemming from the gas phase. Finally, optical spectroscopy in solvent and DRS measurements performed on the supramolecular assembly exhibit similar features identified as three absorption peaks tracing a π → π * electronic transition followed by a vibronic progression, plus a broader band featuring a set of higher energy transitions. Due to both, the weak electrostatic interactions and a lack of π − π interactions in the condensed molecular phase, DR spectra exhibit no major excitonic effect, but a non-rigid redshift of the molecular absorption band compared to the situation in solvent. This observation is found to be consistent with the isomer selection due to the transition from the gas phase to the on-surface condensed phase.

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Adsorption‐induced changes of intramolecular optical transitions:PTCDA/NaCl and PTCDA/KCl

Cited by 13 publications

References 58 publications

Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

Long Vertical Distance Bonding of the Hexagonal Boron Nitride Monolayer on the Cu(111) Surface

Stereoisomeric selection upon adsorption: A structural and optical study of curcuminoid derivatives on ultrathin films of KCl on Au(111) and on bulk KCl(001)

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