Spatial separation of triplet excitons drives endothermic singlet fission

Activating intramolecular singlet exciton fission by altering π-bridge flexibility in perylene diimide trimers for organic solar cells

“…In principle, the trimeric structure allows entropic gain to play a signicant role in the SEF thermodynamics, as literature studies have reported for solid state lms 8,67 and very recently for oligomers. 56 The quantum chemical simulations indeed showed the presence of three multiexcitonic states. For b, the two 1 TT accommodated on adjacent PDIs of the structure, as well as that on the le-most and right-most PDI units, are energetically accessible from S 1 .…”

Geometries and Terahertz Motions Driving Quintet Multiexcitons and Ultimate Triplet–Triplet Dissociations via the Intramolecular Singlet Fissions

“…[28][29] The above pioneering interpretations of the ESP mechanisms may pave a new avenue to clarify how the molecular conformations and their motions drive the spin-conversions and the ultimate T+T generations, both of which are essential but unknown for the photon-to-energy conversion process. In particular, because the J-coupling is anticipated to be sensitive to the T A T B conformations, it is expected that the specific molecular motions or phonon modes may play roles for the ultimate T+T de-coupling, 30 as the vibronic effects. So far, details of the T A T B geometries, the vibration modes and frequencies, and the electronic couplings are unresolved in the iSF systems for generating the quintet multiexcitons and the subsequent T+T dissociations.…”

“…These flat conformations are consistent with a recent ultrafast study of an iSF system; Korovina et al reported that the initial 1 (TT) state conformation possesses the long-range planar structure in the perylene oligomers lined by 1,4-dialkynyl-2,5-bis(ethylhexyloxy)-benzene molecular motif, reflecting electronic delocalized character in the S 1 state. 30 This denotes that the strongly-coupled 5 (TT)s also take on the initial 1 (TT) flat conformations, most likely because the two triplets in the multiexciton are mutually delocalized in the entire planar geometry in Figure 4 to stabilize the multiexcitons rather than in the twisted conformers of TT 2 . The above delocalized feature is very consistent with the weaker ZFS parameters of the D and E values applied in H TTzfs than in the T+T states, as shown in Table S2 to explain the line-shapes of Figure 2.…”

“…This is also in line with the reported proposal that the torsional disorders resulted to form the two separated triplet excitons in the linked perylene oligomers. 30 After such large degrees of the distortions in Figure 5, the two triplet spins can separately be localized to form the biradical characters concentrated around the C6 and C13…”

Porous Shape-Persistent Rylene Imine Cages with Tunable Optoelectronic Properties and Delayed Fluorescence

“…Singlet fission has been observed in solid samples of PDI derivatives. 35 However, twice the triplet energy of a PDI is somewhat above the energy of its S1 state, which leads to an inefficient singlet fission in molecular dimers because the spatial separation of triplet excitons that drives 36 endothermic singlet fission is prohibited. A strong electronic coupling in cofacial PDI dimers typically leads to the formation of unproductive excimer 37 or charge-separated states 28,31 and a slipped stack geometry, observed in PDI thin films, is believed 35 to be crucial for a singlet fission to occur in PDI derivatives.…”