Overlapping of Frontier Orbitals in Well-Defined Dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene and Picene Monolayers

Abstract

Well-defined monolayers with single-crystalline-like molecular arrangements of dinaphtho­[2,3-b:2′,3′-f]­thieno­[3,2-b]-thiophene (DNTT) and picene, which are a new class of organic semiconductors with enhanced intermolecular interactions, were fabricated and characterized. Although both molecules initially form a loosely packed monolayer with a flat-lying molecule, they undergo phase transition into a densely packed monolayer with single-crystalline-like molecular arrangements with increasing molecular density. Upon the phase transition of the monolayer, the highest occupied molecular orbital (HOMO) level of these molecules splits into two features, as suggested from both the ultraviolet photoelectron spectroscopy and density functional theory calculations. The splitting of the HOMO level was observed to be similar to that expected for the molecular arrangement in the single crystal. This splitting, which has not been observed in the polycrystalline film, suggests a substantial overlap of the HOMO in the well-ordered monolayers.

Interface Structure and Evolution of Dinaphthothienothiophene (DNTT) Films on Noble Metal Substrates

“…Interestingly, this packing motif is similar to the molecular arrangement found for the plane of the DNTT bulk crystal structure, which is depicted in Figure d. We note further that the molecular arrangement is also very similar to the dense phase of DNTT on Au(111) reported by Hasegawa et al, although in their study, a precise determination of the structure was not achieved. In their work, they claimed that the compressed monolayer exhibits a similar molecular packing motif as the (110) plane of DNTT, which, however, appears questionable as in that plane, all molecules are additionally tilted with their long axis.…”

“…Since the different phases were in all cases formed at room temperature, the respective energy barrier for a transition from the P‐ML to the HB‐ML during molecule deposition seems not to be very high (see also the data presented in Figure S2 in the Supporting Information showing the transition of the monolayers before and after the critical film thickness). We note that a similar scenario has been proposed for the formation of a dense packed DNTT monolayer on Au(111) (although in the previous study, a tilting was more speculated without any experimental proof). Furthermore, thickness‐dependent structural variations in (sub‐)monolayer films have also been observed before, e.g., for the growth of quaterphenyl thin films on Au(111) .…”

“…While molecules generally are weakly adsorbed on noble metal surfaces such as gold and silver, an additional modulation of the interaction potential occurs on the reconstructed Au(111) surface which can be safely excluded on Ag(111). Hence, making a comparison with the previous growth study on DNTT on Au(111) particularly interesting.…”

“…Despite their importance for device applications, interfaces between DNTT and metals are hardly studied so far. The only exception is the previous work of Hasegawa et al who studied the initial stage of DNTT film growth on Au(111) and reported a transition from an initially diluted phase into a densely packed adlayer which comprises a mixture of flat‐lying and inclined molecules . While this growth scenario is of particular interest, as it would allow adjusting the interface structure to the crystal bulk phase, no clear evidence for such a tilting was given and also the structure of thicker films was not analyzed.…”

Potentiometric Parameterization of Dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene Field‐Effect Transistors with a Varying Degree of Nonidealities

“…[38] After all, the impressive linearity between the square-root I D and V G for the TC devices confirms the outstanding ability of DNTT to form well-ordered molecular films (Figure 2c) with strong electronic coupling between frontier orbitals. [41,42] …”