1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 z Organic & Supramolecular Chemistry Design, Synthesis, Opto–Electrochemical and Theoretical Investigation of Novel Indolo[2, 3-b]naphtho[2, 3-f] quinoxaline Derivatives for n–Type Materials in Organic Electronics Rajesh M. Kamble,* [a] Bharat K. Sharma, [a] Azam M. Shaikh, [a] and Sajeev Chacko [b] A series of seven new donor–acceptor compounds based on indolo[2, 3-b]naphtho[2, 3–f] quinoxaline were synthesized by using Buchwald–Hartwig amination reaction between 12– bromo–9–heptyl–5H–indolo[2, 3–b]naphtho[2, 3–f]quinoxaline- 5,15-(9H)–dione (1) and diaryl/cyclic amine (2–5) and by Suzuki–Miyaura coupling reaction of 1 with aryl boronic acid (6–8). The synthesized molecules were studied to determine their absorption, emission, electrochemical, thermal properties. Theoretical properties were also studied by time dependent density functional theory (TD-DFT). The HOMO and LUMO energy levels of 2–8 are in the range of À6.51 to À6.84 eV and –3.00 to –3.30 eV respectively. LowÀlying LUMO energy levels of 2–8 are very similar to wellÀknown nÀtype materials. On the basis of experimental and theoretical studies synthesized compounds could act as nÀtype materials in organic elec- tronics. Introduction Extensive progress in the field of organic electronics is due to the development of cost–effective organic p–conjugated materials that can be readily accessible from raw materials, through a sustainable synthesis with ease of purification. [1] One of the key step in the synthesis of such kind of p–conjugated molecules is by using Donor–Acceptor (DÀA) architecture. Organic p–conjugated molecules bearing DÀA architecture has builtÀin intramolecular charge transfer (ICT) which allow to tune the opto-electrochemical properties over a wide range by modifying DÀA moieties leading to small band gap semi- conducting materials. [2,3] In the recent past, variety of DÀA type of compounds were reported bearing donor moieties such triarylamine, [4] carbazole, [5] imidazole, [6] indoline, [7] pyrenoimida- zole, [8] indolocarbazole, [9] and electron-deficient/acceptor core compounds such as quinoxaline, [10] pyridopyrazine, [11] benzo- thiadiazole, [12] diketopyrrole, [13] pyridothiadiazole, [14] thienothia- diazole, [15] etc with the broad absorption in visible range of spectrum and used as electroluminescent materials in opto- electronic devices. Indoloquinoxalines (IQ) are important class of ‘N’ containing heterocyclic compounds obtained by the fusion of indole and quinoxaline subunits showing highly attractive biological properties such as anticancer, [16] antiviral, [17] antimicrobial, [18] and antibacterial [19] activities in the field of pharmaceutical research and this became possible as a reason IQ derivatives are observed to interact with DNA by the intercalation of the planar indolo[2, 3-b]quinoxaline moiety between the nucleo- bases. Most of the IQ derivatives functionalized over 8 th or 9 th position of indole subunit reported till date were studied for optoelectronic application but change in electronic properties of IQ molecule by substitution of groups, at quinoxaline segment are very rare and have not been studied extensively. [20] The electronic properties of the IQs can be altered by the introduction of electron-donating or electron-demanding groups on the indole as well as quinoxaline nucleus. The presence of electron-donating groups such as amine/aryl or heteroaryl on the indole nucleus may enhance the donor ability of the indole moiety and increase the D–A interaction with the quinoxaline unit. Alternatively, addition of electron-accepting quinone unit on quinoxaline may result in a bidirectional D–A interaction between the indole, quinoxaline, and auxiliary electron accept- or. Such a tunable molecular structure may be exploited for specific applications requiring donor-acceptor interactions and the resulting electronic properties. Thus in this work, consider- ing the importance of D–A architecture and indoloquinoxalines in mind we have designed and synthesized a series of new dyes 2–8, whose structures are based on indolo[2, 3–b]quinoxa- line skeleton derived from anthraquinone (Figure 1) and studied their detailed photophysical, electrochemical and thermal properties for their possible application in organic electronics. Attempts were also made to understand the electronic structure of newly synthesized dyes using TD-DFT calculations. [a] Dr. R. M. Kamble, Dr. B. K. Sharma, Dr. A. M. Shaikh Department of Chemistry University of Mumbai Mumbai – 400098, India E-mail: kamblerm@chem.mu.ac.in [b] Dr. S. Chacko Department of Physics University of Mumbai Mumbai – 400098, India Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201801208 Full Papers DOI: 10.1002/slct.201801208 6907 ChemistrySelect 2018, 3, 6907 – 6915  2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim