Opto-electrochemistry of pyridopyrazino[2,3- b ]indole Derivatives
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Opto-electrochemistry of pyridopyrazino[2,3-b]indole Derivatives POOJA S SINGH, AKSHATA J SHIRGAONKAR, BHARGAVI K CHAWATHE and RAJESH M KAMBLE* Department of Chemistry, University of Mumbai, Santacruz (E), Mumbai 400 098, India E-mail: [email protected] MS received 25 June 2020; revised 22 August 2020; accepted 4 September 2020
Abstract. Here, pyridopyrazino[2,3-b]indole based D–A assembly was designed and synthesized with modulation of various electron-donating/withdrawing substituent and characterized by various spectroscopic methods. Pyridopyrazino[2,3-b]indole derivatives show inbuilt intramolecular charge transfer (ICT) transition which established D–A building in molecules and induces blue-green emission in the solution state. However, solid-state emission characteristics explore the emission property of some molecules towards aggregationinduced emission (AIE) effect which leads to the formation of emissive nano aggregates in THF/H2O mixture. Alteration of substituent on pyridopyrazino[2,3-b]indole segment effectively tune electrochemical property and resulting LUMO energy level was found to be comparable with reported electron transporting/ntype materials. These properties and good thermal stability indicate that molecules have the potential to be used as solid-state emitter and n-type materials in optoelectronic devices. Keywords. Pyridopyrazino[2,3-b]indole; intramolecular charge transfer; donor–acceptor; HOMO–LUMO energy level; aggregation-induced emission; n-type materials.
1. Introduction In recent years, smaller heterocyclic compounds having donor–acceptor (D–A) interaction set up one of the largest areas of research in organic electronics1–3 due to their tuneable optoelectronic property, well–defined structures, ease of purification, solubility in a wide range of organic solvents, thermal stability and lowcost solution processing techniques.4 In addition, intramolecular charge transfer (ICT) feature of these systems is advantageous to tune the required luminescence in a molecule. However, a major drawback of D–A molecules having disc-like shape/planar geometry is quenched emission in concentrate/aggregate/solid-state which leads to aggregation-caused quenching (ACQ) phenomenon.5,6 Planar geometry of such system increases intermolecular p–p stacking interactions which arouse the non-radiative relaxation process. Hence, this debases the solid-state emission of the molecule which is generally required for the construction of highly efficient non-doped organic lightemitting diodes (OLED’s) or bio-imaging
application.1,7 Hence Tang and his co-worker proposed a novel idea of ‘‘aggregation-induced emission’’ (AIE)8 which can tackle the problem associated with an ACQ effect by a strategy of restricted intramolecular rotation (RIR) and conformational changes of molecules in its aggregate state. Tang suggests, AIE, usually observed in non-planar, propeller-shaped luminogens that were almost non-fluores
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