Triplet-Pair States in Organic Semiconductors

Abstract

Entanglement of states is one of the most surprising and counterintuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic semiconductor materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which consists of a pair of localized triplet excitons coupled into an overall spin-0, -1, or -2 configuration. The most widely analyzed of these is the spin-0 pair, denoted1(TT), which was initially invoked in the 1960s to explain delayed fluorescence in acene films. It is considered an essential gateway state for triplet-triplet annihilation and the reverse process, singlet fission, enabling interconversion between one singlet and two triplet excitons without any change in overall spin. This state has returned to the forefront of organic materials research in recent years, thanks both to its central role in the resurgent field of singlet fission and to its implication in a host of exotic new photophysical behaviors. Here we review the properties of triplet-pair states, from first principles to recent experimental results.

Optical Projection and Spatial Separation of Spin Entangled Triplet-Pairs from the S1 (21Ag-) State of Pi-Conjugated Systems

“…However, this feature exhibits rapid decay which is not matched by corresponding growth in the band at 600 nm assigned to the 2 1 Ag -/ 1 (TT) state in carotenoid aggregates 52,77 (SI, Figure S13). Any pushinduced effects in possible dark/impurity states thus have no connection to the 'freeing' of triplet-pairs.…”

Electron spin polarization generated by transport of singlet and quintet multiexcitons to spin-correlated triplet pairs during singlet fissions

“…25 ESP was interpreted using the sublevel-selective quintet conversion by the zero-eld splitting (ZFS) interaction at the singlet-quintet level-crossing in the presence of negative exchange coupling (J) during triplet exciton-diffusion and subsequent re-encounter in the highly disordered region, causing modulation of the J-coupling to result in spontaneous 5 (TT) generation. 25 Interestingly, transport of spin-entangled multiexcitons 20,[29][30][31] by the dissociative exciton diffusion has been observed using ultrafast transient absorption imaging of pentacene crystals 32 and by the magnetic eld effect on the uorescence time-proles. Although such transportation of spin-entanglements is key to elucidate the dissociation mechanism and to apply in quantum information science, [33][34][35] no direct evidence for the transportation of spin-entanglements has been found in the separated T + T state with the singlet and quintet characters.…”

Multiexcitonic Triplet Pair Generation in Oligoacene Dendrimers as Amorphous Solid‐State Miniatures

“…In a recent decade, singlet exciton fission (SF) process which generates multiexcitonic triplet pair in organic semiconducting materials has attracted great attention since the exciton multiplication process converting a singlet exciton into two triplets effectively compensates for thermal energy losses [1–10] . Recently, Einzinger et al.…”