Abstract
Self-organization in mono- and bilayers on HOPG of two groups of benz[5,6]acridino[2,1,9,8-klmna]acridine derivatives, namely, 8,16-dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines with an increasing alkoxy substituent length and 8,16-bis(3- or 4- or 5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines, i.e., three positional isomers of the same benzoacridine, is investigated by scanning tunneling microscopy. The layers were deposited from a solution of the adsorbate (in hexane or dichloromethane) and imaged ex situ at molecular resolution. In all cases, the resulting two-dimensional (2D) supramolecular organization is governed by the interactions between large, fused heteroaromatic cores that form densely packed rows separated by areas covered by substituents. In 8,16-dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines, the alkoxy substituents, separating the rows of densely packed cores, are interdigitated. An increasing substituent length leads to an intuitively expected increase in this 2D unit cell parameter that corresponds to the orientation of the substituent in the monolayer. In the case of 8,16-bis(3- or 4- or 5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine positional isomers, the self-assembly processes are more complex. Although the determined 2D unit cell is in all cases essentially the same, the role of alkylthienylene substituents in layer formation is distinctly different. Thus, the formation of monolayers and bilayers is very sensitive to isomerism. 8,16-Bis(5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine is capable of forming the most stable monolayer and the most labile bilayer. In the case of 8,16-bis(3-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine, an inverse phenomenon is observed leading to the most labile monolayer and the most stable bilayer. These differences are rationalized in terms of dissimilar molecular geometries of the studied isomers and different interdigitation patterns in their 2D supramolecular structures.
Highlights
Nonlinear and fused azaacenes are promising materials for application in organic electronics as components of active layers in field effect transistors (FETs)[1−4] and light-emitting diodes (LEDs).[5]
We present a detailed investigation of these self-assembly phenomena, analyzing the effect of the substituent length on the 2D self-organization of the studied alkoxy derivatives
A clear dependence of the submolecular Scanning tunneling microscopy (STM) contrast on the tunneling current direction was noted. It could be directly correlated with differences in the location of electronpoor and electron-rich parts of the molecules, reflected by the distribution of the molecular orbitals (LUMO and HOMO) in their central fused aromatic−azaacene cores
Summary
Nonlinear and fused azaacenes are promising materials for application in organic electronics as components of active layers in field effect transistors (FETs)[1−4] and light-emitting diodes (LEDs).[5]. We demonstrated that these derivatives can be relatively obtained from old and almost forgotten nitrogen atom-containing vat dyes such as indanthrone (6,15-dihydrodinaphtho[2,3-a:2′,3′-h]phenazine5,9,14,18-tetraone) or flavanthrone (benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine-8,16-dione) in a two-step, one-pot reaction involving reduction of their carbonyl group followed by O-alkylation or another type of substitution.[6−8] These derivatives are technologically attractive because they are solution processable and exhibit excellent photo- and electroluminescence.[7,9] In addition, they are electrochemically interesting showing electrochromic properties associated with the reversibility of their reduction All of these electronic and optoelectronic properties facilitate their application in various types of organic electronic devices.[7,9,10]. The necessary data of DFT calculations were retrieved from output files using GaussSum 2.2.32 All necessary initial geometries and final graphics (molecular orbitals) were generated in GaussView 5.0.33
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