Molecular modelling and electronic structure calculations of novel organic semiconducting materials

Thesis submitted in the fulfillment of the requirement for the degree of Doctor of Philosophy by Ankit Kargeti (1800211C601) Under the supervision of Dr. Tabish Rasheed and Dr. Shamoon Ahmad Siddiqui Doctor of Philosophy 2023

Organic semiconducting materials (OSMs) have received lot of attention in the last three decades due to their highly versatile nature. They are considered to be future materials for development of ultra−miniaturized electronic devices. Such devices are classified under the general definition of organic electronics (OE). OE is based on OSMs which may be small molecules, oligomers, or polymers. They have opened the path for development of molecular−level electronics or moletronics. Such devices can be fabricated on flexible substrates due to flexible nature of OSMs, making them foldable in nature. OSMs have been predicted to have the capability to revolutionize modern world of computing and digital electronics. Hence, they have garnered the interest of researchers as potential future alternative to silicon-based electronics. At present, OSMs are still far from replacing inorganic materials in electronic devices entirely because of their lower comparative functionality. Discovery and research into novel OSMs are expected to bridge the gap in near future.
Present thesis deals with the modelling and simulation of novel OSMs by employing density functional theory (DFT). It aims to predict and investigate novel OSMs for various electronic applications. In order to achieve this objective, both ground and excited state properties have been simulated by utilizing quantum chemical calculations. First chapter focuses on introducing basic concepts related to OSMs by discussing its basic structure and properties. Second chapter describes the methodology used in thesis by providing details of all fundamental theories related to quantum chemical calculations. Charge transport mechanism of various OSMs having applications as different electronic components have also been reviewed in this chapter. Third chapter deals with the molecular modelling of novel organic molecules having potential application as organic single molecule diodes (OSMDs). These molecules are based on Aviram and Ratner’s D−σ−A model. In this chapter, effect of external EF has been elucidated on subject molecular properties. Fourth chapter discusses modelling of molecules suitable for use as organic
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field effect transistors. These molecules have D−π−A type structures. Discussion has been carried out on the basis of calculated reorganization energies of holes and electrons. This discussion involves the Marcus theory of charge transfer in organic molecules. Fifth chapter deals with modelling of novel organic dye molecules suitable as dye photosensitizers in dye sensitized solar cells (DSSCs). Comprehensive investigations on the effect of increasing donor units in Dn−π−A (n = 1, 2, 3) type molecules have been carried out. Particularly, the impact of double donor and triple donor moieties on dye photosensitizer efficiency has been discussed. Sixth chapter discusses the design of novel D−πm−D (m = 1, 2) structures and effect of bridging on charge transport properties. Seventh chapter concludes the thesis by providing the future scope of present work.