Spin dynamics of thiophene-fused π-systems with delayed emission.

Triplet excited states in organic molecules are generally optically inactive due to spin-forbidden transitions to the singlet ground state. Recent studies have extensively investigated triplet states to circumvent limitations imposed by spin statistics in organic light-emitting diodes. Room-temperature electrophosphorescence and electrofluorescence have previously been observed in thienyl-substituted phenazines without heavy metals; however, phosphorescence was absent when spin density was localized on the thiophene units, despite the expected heavy-atom effect from the sulfur atom.