In this Dissertation, we study the mechanism of singlet fission (SF) with an emphasis on utilizing covalent and noncovalent interactions to control and understand the role of inter- and intramolecular interactions that impact the relevant electronic states. We are particularly interested in how these states mix, as such mixing can open new photophysical and excited state relaxation pathways in organic materials. Our research has focused heavily on pentacene derivatives as a model system for understanding the SF mechanism. We have explored various pentacene monomers, dimers, and longer oligomers, and used them to form supramolecular assemblies via noncovalent interactions, as well as other novel aggregate types. We have also attempted to incorporate pentacene into metal-organic frameworks (MOFs) and, along the way, studied a variety of other fluorescent MOFs to better understand their photophysics. Additionally, we investigated other unique molecules such as cumulenes.Chapter 1 provides an introduction to the key topics necessary for understanding this Dissertation. Chapter 2 outlines the experimental techniques used to study SF and other excited-state processes in organic molecules and MOFs. In Chapter 3, we report the first ever direct photoexcitation of the 1TT intermediate state. Chapter 4 demonstrates how supramolecular self-assembly can modulate the balance of inter- and intramolecular couplings relevant to SF, while Chapter 5 shows how similar molecules can access a broader aggregate space that enhances the 1TT oscillator strength through state mixing. Chapter 6 examines the photophysics of MOFs, including how intermolecular coupling can be tuned to create different excited-state relaxation pathways in the same organic linker and how disorder affects materials typically considered crystalline. This Chapter concludes with our attempts to incorporate pentacene – and previously anthracene and tetracene – into MOF pores. Chapter 7 explores the photophysics of cumulenes, from isolated molecules to MOF-incorporated structures. A final summary and outlook is provided in Chapter 8.