Hydrogen‐Bonding Fingerprints in Electronic States of Two‐Dimensional Supramolecular Assemblies

Abstract

During the last years, the transfer and adaptation of the concepts of supramolecular chemistry [1][2][3] to the formation of twodimensional (2D) supramolecular nanostructures on surfaces has become a particularly active area of research. A variety of one-dimensional (1D) and 2D hydrogen-bonded structures have been reported, [4][5][6][7] ranging from homomolecular systems to binary assemblies on well characterized single-crystal surfaces. [8][9][10][11][12] In particular, regular heteromolecular assemblies based upon hydrogen bonding have been successfully formed by coadsorption of molecular species exhibiting complementary functional amine/imide end-groups on nanostructured template substrates, such as vicinal Au(111) surfaces. [13,14] So far, most studies concerned the exploration and description of basic pattern formation using simple prototype building blocks. With the aim of achieving better control of the structures resulting from hydrogen-bond-driven self-assembly, recent efforts have been devoted to obtain a thorough understanding of all relevant physico-chemical interactions in these systems. [15][16][17] A very important, but hitherto less addressed question is that of the impact of hydrogen bonding on the molecular electronic structure. [18][19][20] A quantitative understanding of the energetics and electronics of different hydrogenbonding configurations will contribute to better control in the fabrication of specific supramolecular assemblies, and might ultimately allow the design of the electronic properties of hydrogen-bonded supramolecular architectures by engaging the building blocks in specific hydrogen-bonding configurations.Chemical bonding is intimately related to the valence electronic structure, but changes in the local molecular orbital structure due to different hydrogen-bonding environments in 2D supramolecular assemblies have not been explored in detail so far.[21] Herein, by comparing distinct hydrogen-bonding environments for two molecular species, we provide the spectroscopic fingerprints of such changes, which are explained in terms of charge polarization at the molecular scale induced by anisotropic strong threefold hydrogen bonds. We present a combined experimental and theoretical study of the unoccupied electronic states of 2D mono-and bicomponent assemblies of 1,4-bis-(2,4-diamino-1,3,5,-triazine)-benzene (C 12 H 12 N 10 , BDATB) and 3,4,9,10-perylenetetracarboxylic diimide (C 24 H 10 N 2 O 4 , PTCDI) on Au(111). The self-assembled supramolecular structures of PTCDI and BDATB were characterized by scanning tunneling microscopy (STM) as described in detail elsewhere. [14] In the present study, the electronic structure of both PTCDI and BDATB molecular species involved in distinct chemical environments is characterized by means of low-temperature scanning tunneling spectroscopy (STS) [see the Supporting Information for experimental details].STM images such as those shown in Figures 1 a-c suggest that, apart from weak lateral hydrogen bonds, homomolecular PTCDI and BDATB assemblies e...

Spectroscopic Fingerprints of Work-Function-Controlled Phthalocyanine Charging on Metal Surfaces

“…19 In the blends, changes in F 16 CuPc's energy-level alignment may arise from the new supramolecular environment and the new intermolecular interactions with the surrounding H-bonded PEN molecules. 19,21,34,35 However, as recently shown, those changes may be dominated (compensated or even reversed) by changes in the work function, which for the blends corresponds in a good approximation to a weighted average of the work functions associated with layers of each of the molecules separately. 19,20 The work function of the 1:2 blend on Cu(111) is slightly lower than that of F 16 To confirm this assumption, valence band photoemission and NEXAFS spectra were measured for the blend.…”

Multi‐Component Organic Layers on Metal Substrates

“…This rearrangement can have a significant impact on the molecular electronic structure. In calculations of free‐standing layers of an H‐bonded BDATB‐PTCDI system (3,4,9,10perylenetetracarboxylic diimide and 1,4‐bis‐(2,4‐diamino‐1,3,5,‐triazine)benzene), González‐Lakunza et al found that charge rearrangement leads to significant shifts of a few hundred meV in BDATB and PTCDI's molecular levels . The levels shift in opposite directions for each molecule, moving down in energy for the typical acceptor molecule PTCDI and moving up in energy for BDATB, in agreement with the STS findings of the blends on Au(111).…”

Metal-organic interface functionalization via acceptor end groups: PTCDI on coinage metals

“…The effect of these interactions in binary compounds of donor-acceptor molecules [4,5] deposited on metal substrates has been of particular interest, since they strongly modify the interface electronic structure, appearing as a suitable way to tune the substrate work function [6,7]. In pure compounds though, the specific effect of moleculemolecule interactions is more elusive, in particular for the electronic properties [8][9][10][11]. In this work, we provide a detailed interpretation of the interface characteristics within the context of intermolecular versus molecule-substrate interactions by presenting a comprehensive study of perylene-3,4,9,10tetracarboxylic diimide (C 24 H 10 O 4 N 2 , PTCDI) [12,13] adsorbed on the (111) surface of the coinage metals.…”