Effects of electronegative substitution on the optical and electronic properties of acenes and diazaacenes

Abstract

Large acenes, particularly pentacenes, are important in organic electronics applications such as thin-film transistors. Derivatives where CH units are substituted by sp 2 nitrogen atoms are rare but of potential interest as charge-transport materials. In this article, we show that pyrazine units embedded in tetracenes and pentacenes allow for additional electronegative substituents to induce unexpected redshifts in the optical transitions of diazaacenes. The presence of the pyrazine group is critical for this effect. The decrease in transition energy in the halogenated diazaacenes is due to a disproportionate lack of stabilization of the Homo on halogen substitution. The effect results from the unsymmetrical distribution of the Homo, which shows decreased orbital coefficients on the ring bearing chlorine substituents. The more strongly electron-accepting cyano group is predicted to shift the transitions of diazaacenes even further to the red. Electronegative substitution impacts the electronic properties of diazaacenes to a much greater degree than expected.

Theoretical study of stability and charge-transport properties of coronene molecule and some of its halogenated derivatives: A path to ambipolar organic-based materials?

“…3 Many known organic materia) E-mail: jc.sancho@ua.es b) E-mail: aj.perez@ua.es als show excellent p-type performance, mainly elucidated due to the intense research performed in last years, with the selection of materials for n-type behavior being now under closer scrutiny. [4][5][6] The path followed for achieving n-type organic semiconductors is based on the large body of knowledge existing for corresponding p-type systems. For instance, functionalization of the molecule with active electron-withdrawing groups is a recurrent strategy, be these groups cyano, imide, or halogen atoms, as well as heteroatom replacements of the carbon atoms within the molecular backbone.…”

Stable Hexacenes through Nitrogen Substitution

“…[8,12] To investigate this issue more closely, we performed quantum chemical calculations on model systems of these heteroacenes (trimethylsilylethynyl instead of TIPS-ethynyl; see the Supporting Information for details). We plotted the LUMO energies versus the reduction potentials and found a linear correlation of the two quantities (Figure 2).…”

An Efficient Synthesis of Tetraazapentacenes

“…Oxidation with MnO 2 quantitatively transforms these products into the diazaacenes 6 a,b (Scheme 1). [3,4] At temperatures above 250 8C, reaction mixtures of 7 with 2 a, with or without [(Ph 3 P) 2 PdCl 2 ] present, give rise to undefined, tarry decomposition products. Upon reaction of the mixture of 7 with 2 a-c in Hünig base in the presence of Pd(OAc) 2 or [Pd(dba) 2 ] (dba = dibenzylideneacetone) and the ligands L1-L5 at 120 8C for 16 h, we obtained the desired coupling products 8 a-c (Scheme 2).…”

“…The synthesis of 10 fails, perhaps as it might be a strongly Scheme 1. Synthesis of azaacenes according to Hinsberg and Appleton et al [1,3,4] Scheme 2. Palladium-catalyzed synthesis of 9 a-c and the structure of the ligands L1-L5.…”