Interesting how "through a process called singlet exciton fission" and other article "General Formula for Bi-Aspheric Singlet Lens Design Free of Spherical Aberration" [1] both deal with Singlets. Odd coincidence of the day.
FYI they are totally different "singlets", a singlet exciton refers to the spin state of the particle (as opposed to a triplet exciton, which has a different total spin). A singlet lens is just a lens with a single simple component.
[1] https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-31-9...