The Effects of Noncovalent Interactions on Surface Structures Formed by Diketopyrrolopyrrole Pigment and Its Alkyl-Derivatives on HOPG Substrate

Abstract

Two-dimensional self-assembled structures formed by diketopyrrolopyrrole Pigment Red 254 (3,6-bis(4-chlorophenyl)-2,5-dihydropyrrolo [3,4-c]pyrrole-1,4-dione) and its alkyl-derivatives at the liquid-HOPG interface were investigated by scanning tunneling microscope (STM). Pigment Red 254 is found to form two different surface structures (crystal-like structure and solvated crystal-like structure). Furthermore, in order to investigate the effect of hydrogen bonding, alkyl-derivatized Pigment Red 254 (PR-2Cn, n: alkyl chain length) were synthesized, and their self-assembled structures were analyzed. We found that surface structures of PR-2Cn varied depending on the intermolecular and moleculesubstrate van der Waals interactions arising from the n-alkyl chains introduced instead of hydrogen bonding. Shorter alkyl chains of PR-2C10 resulted in the formation of multi domains. On the other hand, PR-2C12, PR-2C14, and PR-2C16 molecules that have longer alkyl chains formed stable single domain structures.Surface molecular structures are very important in understanding the mechanism of phenomena involving surfaces and/ or interfaces, such as catalysis, tribology, photochemistry, electrochemistry, etc.14 The major function of dyes and pigments is to selectively absorb and reflect a certain wavelength region of visible light, and exhibit color. Usually they function at a substrate surface, i.e., they are expected to self-assemble and be adsorbed firmly onto the substrate. The assembled structures of the pigments are essentially important to understand their coloring function, since they have strong influence on the strength of adsorption and absorption spectra. Hence, the surface structures formed by dye and pigment molecules have been investigated intensively.510 Pigment Red 254 (3,6-bis(4-chlorophenyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) is a brilliant red pigment which has diketopyrrolopyrrole (DPP 1113 ) chromophore (Figure 1a), and is used in many coloring items, such as color filters, automobile paint, printing ink, etc. Because of its frequent uses, the coloring functions and the structural analyses of Pigment Red 254 have been studied worldwide.1417 However, more specific information on the self-assembled twodimensional structure formed by Pigment Red 254 is still in needed to understand its coloring function.Scanning tunneling microscope 18 (STM) is a tool that is capable of resolving surfaces in molecular or atomic resolution, and thus STM is used as a powerful tool to analyze surface structures. STM images can be recorded not only under ultrahighvacuum (UHV) conditions, but also at the air-substrate and liquidsubstrate interfaces. This means that STM is capable of observing molecules at ambient conditions, at which they function. In general, noncovalent interactions such as hydrogen bonds, van der Waals interactions, and dipoledipole interactions stabilize the molecules on the substrate. Therefore, adsorbed molecules form a variety of two-dimensional structures depending on the noncovalent interactions th...

H-Bonding Control of Supramolecular Ordering of Diketopyrrolopyrroles

“…On the other hand, the enantiomeric H-bonded lamellae interact with each other via nondirectional weak vdW contacts of the Ph rings, and thus, the chiral information in not transmitted along this direction. Indeed, a structurally related bis­( p -chlorophenyl)­DPP, in which phenyl rings expeirence stronger dipole–dipole interactions, forms homochiral 2D domains on HOPG …”

“…Indeed, a structurally related bis(p-chlorophenyl)DPP, in which phenyl rings expeirence stronger dipole−dipole interactions, forms homochiral 2D domains on HOPG. 41 Self-Assembly of DTDPP. Isostructural to DFDPP, DTDPP forms a similar co-assembled lamellar structure (a = 1.0 ± 0.1 nm, b = 2.2 ± 0.1 nm, and α = 80 ± 2°) at the octanoic acid−HOPG interface (Figure 3).…”

A Convenient Synthesis of Diketopyrrolopyrrole Dyes

“…Pigment Red 254 (also known as Ferrari red) is an inexpensive commercial DPP pigment. However, it has scarcely been used as precursor to other DPP derivatives and the reported transformations are mainly N -alkylations [ 54 , 55 , 56 , 57 ]. Although it contains two 4-chlorophenyl groups that can be used to get access to other DPP derivatives by direct substitution of the chlorine atoms, this approach has been rarely used [ 28 , 58 , 59 , 60 ].…”

Surface Structures Formed by a Copper(II) Complex of Alkyl-Derivatized Indigo

“…“2D chirality” of the adsorbed molecules on the substrate has been intensively studied [ 18 , 19 , 20 ]. When a prochiral molecule adsorbs onto a substrate, the molecular inversion is restricted and the adsorbed molecules can be distinguished as enantiomers (λ and δ in Figure 4 ).…”