Singlet fission has the potential to significantly enhance the efficiency of photovoltaic light harvesting of silicon solar cells beyond the Shockley-Queisser limit. The progress of this technology has been hindered by the limited selection of suitable molecules that can undergo singlet fission, and the methods we use to screen new materials. This thesis is constructed in two parts: the investigation of two indigoids in their candidacy for singlet fission, and the use of an alternative method, modulated magnetic field effects in photoluminescence (modMPL), as a potential screening tool for materials.

After relevant theoretical and experimental background is discussed in Chapters 2 and 3, Chapter 4 presents an alternative method for investigating singlet fission: modMPL. We employ this highly sensitive technique to examine thin films of the well-studied singlet fission system, TIPS-tetracene. This technique reveals complex lineshapes describing the spin physics in great detail. ModMPL is a rapid, low-degradation technique, that greatly enhances the screening of new potential materials. In particular, it allows comparison of sample morphologies and their impacts on singlet fission dynamics in a way that is not currently available with conventional screening techniques. A discussion of how to simulate and understand modMPL lineshapes is included in Chapter 5.

Secondly, we make use of ultrafast transient absorption spectroscopy to investigate two indigoids, a novel aza-cibalackrot (Chapter 6) and thienoisoindigo (Chapter 7). Both derivatives of indigo dyes, they are highly attractive candidates for singlet fission due to their superior photostability, high extinction coefficient, and ideal predicted triplet energy. We explore these new, versatile, potential molecular families for their singlet fission capability. Furthermore, we discuss an alternative molecular design principle for creating singlet fission candidates with greater photostability, which may then be applied to other molecular families in the search for singlet fission chromophores.