Persistent Multiexcitons from Polymers with Pendent Pentacenes

Abstract

Singlet fission has emerged as a key mechanism of exciton multiplication in organic chromophores, generating two triplet excitons from a single photon. Singlet fission is typically studied in crystalline films or in isolated dimers. Here, we investigate an intermediate regime where through-space interactions mediate singlet fission and triplet pair recombination within isolated polymer chains. Specifically, we investigate how appending pentacenes to a polynorbornene backbone can lead to macromolecules that take advantage of through-space π−π interactions for fast singlet fission and rapid triplet pair dissociation. Singlet fission in these systems is affected by molecular dynamics, and triplet−triplet recombination is a geminate process where the rate of recombination scales with molecular-weight. We find that these pendent pentacene polymers yield free triplets with lifetimes that surpass those of crystalline chromophores in both solution as isolated polymers and in thin films.

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

“…Previously, Yablon et al. described the distinct ESA band located between the broad ESA bands in the transient absorption spectrum of pentacene polymers by the linear combination of transient absorption signals of S 1 and 1 TT states [69] . Similarly, the transient absorption spectrum of the hexamer is well accounted for by the quasi‐equilibrium between the two states, however, excited‐state populations remain at the S 1 state much dominantly (Figure 4).…”

Singlet fission in a hexacene dimer: energetics dictate dynamics

“…[10][11][12][13][14][15][16][17][18] Dimers serve as model systems to study singlet ssion. They represent the fundamental smallest number of chromophores required for SF and varying the connectivity between the chromophores can lead to insightful structure-property relationships of the constrained excitons, from the generation, [19][20][21][22] separation, [23][24][25][26] and recombination [27][28][29][30] of triplet states, to the elucidation of the bound triplet pair state. [31][32][33][34] It has been established that molecular vibrations play a key role in mediating singlet ssion in both oligoacene molecular crystals (intermolecular singlet ssion, xSF) and in acene intramolecular singlet ssion (iSF) compounds.…”

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

“…[67,68] Previously,Y ablon et al described the distinct ESA band located between the broad ESA bands in the transient absorption spectrum of pentacene polymers by the linear combination of transient absorption signals of S 1 and 1 TT states. [69] Similarly,the transient absorption spectrum of the hexamer is well accounted for by the quasi-equilibrium between the two states,h owever, excited-state populations remain at the S 1 state much dominantly (Figure 4). Since asinglet excitation effectively migrates within the hexamer by Fçster energy transfer, astochastic SF process is suggested at ah ot spot of relatively efficient electronic coupling for SF process which is developed by steric effects between bulky TIPS-pentacenes.Afterwards,remaining S 1 state populations are transferred to multiexcitonic triplet pair states at aslower rate of 5.6 ns which is analogous to SF rates in TP2 and QP2.…”