Multiexciton Dynamics Depending on Intramolecular Orientations in Pentacene Dimers: Recombination and Dissociation of Correlated Triplet Pairs

Abstract

Pentacene dimers bridged by a phenylene at ortho and meta positions [denoted as o-(Pc) and m-(Pc)] were synthesized to examine intramolecular orientation-dependent multiexciton dynamics, especially focusing on singlet fission (SF) and recombination from correlated triplet pairs [(TT)]. Absorption and electrochemical measurements indicated strong intramolecular couplings of o-(Pc) relative to m-(Pc). Femtosecond and nanosecond TA measurements successfully demonstrated efficient SF in both dimers. In contrast, the dissociation process from the (TT) to the individual triplets [(2 × T)] was clearly observed in m-(Pc), which is in sharp contrast to a major recombination process in o-(Pc). Time-resolved electron spin resonance (TR-ESR) measurements demonstrated that the recombination and dissociation proceed from the quintet state of (TT) in m-(Pc). The rate constant of the SF was 2 orders of magnitude greater in o-(Pc) than that in m-(Pc) and was rationalized by enhanced electronic coupling between adjacent HOMOs of the Pc units.

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

“…1) generation mechanism from the S 1 S 0 state. 8,[11][12][13][14][15][16][17] More importantly, elucidation of the TT / T + T dissociation mechanism is highly Fig. 1 Schematic representation of the spin-correlated triplet pair (SCTP) state of 1,3,5 (T + T) generated by the SF in thin films of TIPS-Pn by the triplet energy transfer via the TT state.…”

“…Dissociation time constants ranging from subpicosecond to microsecond regions are reported. [16][17][18][19][20][21][22][23][24][25] However little is known about how the T + T dissociation or the decoupling 12,16,24 occurs from the strongly coupled TT state.…”

“…1, the strongly coupled singlet TT state is known to be initially generated from the S 1 S 0 state. Generation of the quintet state in the triplet-triplet pair 17,22,23,[25][26][27][28] has been reported and is thought to be essential for preventing the loss of the SF-born multiexciton through the singlet channels. Using the timeresolved electron paramagnetic resonance (TREPR) method for TIPS-tetracene thin lms, Weiss et al 26 characterized the SFinduced strongly-coupled quintet of 5 (TT) in Fig.…”

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.…”

Quintet-triplet mixing determines the fate of the multiexciton state produced by singlet fission in a terrylenediimide dimer at room temperature

“…Additionally, the (T 1 T 1 ) states generated by SF are potential sources of four entangled spins for applications in quantum information science. Current studies on SF have focused on elucidating the mechanism and determining the nature of the intermediate electronic state with recent efforts focused on understanding the spin dynamics of the (T 1 T 1 ) state and the processes leading to long-lived uncoupled triplet excitons (4)(5)(6)(7)(8)(9).…”