Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Rai, Neeraj

Committee Member

Gwaltney, Steven

Committee Member

Kundu, Santanu

Committee Member

Meng, Dong

Date of Degree

11-25-2020

Original embargo terms

Worldwide

Document Type

Dissertation - Open Access

Major

Chemical Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Dave C. Swalm School of Chemical Engineering

Abstract

Organic open-shell materials, which are responsive to external stimuli; such as light, electronic field, magnetic field, etc., are subject to intensive studies in recent years for their potential application in the field of organic solar cells, semiconductors, supercapacitors, singletission, non-linear optical (NLO), spintronics, and magnetic materials. As the materials with an open-shell diradical (two unpaired electrons) or polyradical (multiple unpaired electrons) character have a significant promise for next-generation optoelectronics, magnetic, and spintronic devices, it is of paramount importance to design suitable materials with tunable electronic properties. Also, a proper understanding of the molecular topology with electro-magnetic properties and correlate with quantum functionalities can move forward the field of organic photovoltaics and optoelectronics. Here, we show that controlling the radical character based on the different molecular scaffolds can lead to materials from closed-shell (all electrons are paired) low-spin (singlet state) to intermediate open-shell (multi)radical state to high-spin (triplet state) ground-state in the pristine form. In this regard, several organic donoreptor (D-A) polymeric and small molecular systems are designed and characterized. We find that the diradical character is ubiquitous in the narrow bandgap organic materials. Based on this design rule, we have reported open-shell dyes for dye-sensitized solar cells (DSCs), which show significantly red-shifted absorption in the NIR than the closed-shell counterpart dyes. Our work on the alternating D-A polymers indicate stabilization of the high-spin triplet ground-state in the neutral form, not reported for D-A type polymers. A significant delocalization of the unpaired electrons provides thermodynamic stability of the polymer, which when used in supercapacitors, a best-in-class energy density, and a long cycle life are observed. Also, we find that the spin topology can be modulated by careful selection of molecular scaffold in the extended pi-conjugated D-A polymers. Furthermore, our study on D-A macrocycles indicates that the antiferromagnetic (AFM) couplings between the unpaired electrons can be tuned by thiophene pi-spacer, developing a record polyradical character in the macromolecular systems.

URI

https://hdl.handle.net/11668/20879

Sponsorship

National Science Foundation (NSF) under grant no. OIA-1757220

Comments

Diradicals||Donoreptor polymers||High-spin||Macromolecules||NIR dyes||Polyradicals

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