“…Various strategies have been suggested for biasing the fate of S 1 (2 1 A g -) toward triplet production over internal conversion, such as engineering an enhanced ''triplet-pair'' weight into the S 1 (2 1 A g -) wavefunction with donor-acceptor copolymers, 26 and exploiting polymer-polymer interactions to extract long-lasting triplet states. 46,47 Interestingly, when SF does occur in systems expected to have relevant S 1 (2 1 A g -) states, the optical signatures of this intervening singlet are not observed, 18,[48][49][50][51][52] and its proposed role in fission remains controversial. 26,35,53,54 Although, several groups have shown that some polymers, all the way back to polyacetylene 35,39 have triplet-pair-like states similar to 2 1 A g -, 48,55 the general design strategy has been to avoid ''dark'' 2 1 A g states for efficient fission.…”