Exergonic Intramolecular Singlet Fission of an Adamantane-Linked Tetracene Dyad via Twin Quintet Multiexcitons

Abstract

An adamantane-linked tetracene dyad (Tc-Ad-Tc) undergoes exergonic intramolecular singlet fission (SF), producing longlived (t = 175 µs) and high-energy (2 ´ 1.03 eV) multiexciton. Time-resolved absorption, fluorescence decay, and electron paramagnetic resonance (EPR) spectroscopic analysis revealed that the long-lived triplet species is generated in this system via correlated triplet pair having singlet and quintet characteristics. Time-resolved EPR analysis revealed formation of syn-and anti-conformers in the quintet, i.e. 5 ( 3 Tc-Ad-3 Tc)*. The quintet generation requires small conformational motion to induce singlet-quintet spin relaxation. The presence of aliphatic linkages, like the rigid adamantane group, may enable effective conservation of intrinsic high S1 and T1 levels of the original monomers, moderate bridge-mediated s-p interaction leading to exergonic intramolecular SF involving 1 Tc*-Ad-Tc ® 1 ( 3 Tc-Ad-3 Tc)*, and prevention of undesirable triplet-triplet annihilation, finally result in long-lived and high-energy multiexciton.

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

“…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.…”

Probing the Wave Function and Dynamics of the Quintet Multiexciton State with Coherent Control in a Singlet Fission Material

“…Interacting triplet-pair states are key intermediates in photocatalysis [1], photon up-conversion [2], recombination in light-emitting diodes [3][4][5], as well as the process of singlet fission [6,7]-the production of two spin-1 triplet excitons from an initial spin-0 singlet exciton, a process which has received great interest for its potential in photovoltaics [8][9][10][11]. Recently, it has been demonstrated that the biexciton generated by the fission process can evolve in time to form a long-lived pair state with total spin S ¼ 2: a spin-quintet state [12][13][14][15][16][17][18][19]. This quintet state is intriguing for several reasons.…”

Long-lived Triplet State Formation Caused by Intramolecular Energy Hopping in Diphenylanthracene Dyads Oriented to Undergo Efficient Triplet–Triplet Annihilation Upconversion

“…Recently, it was reported that covalently-linked dyads of π-conjugated systems have remarkably large tT. 12,14,22 To gain further insights into the TTA-UC of the three dyads, tT values of DPA-C1-DPA, DPA-C2-DPA, and DPA-C3-DPA in degassed CH2Cl2 were determined using PtOEPsensitized transient absorption analysis. The tT value for 3 DPA* was determined to be 190 µs by analysis of the 450-nm decay profile (Fig.…”

“…Thus, new approaches that lead to improvement of the efficiencies of the TTA process are important because they are bound to serve as the basis of innovative strategies for the design of potentially important TTA-UC systems. By using time-resolved spectroscopic studies, several factors that improve the efficiency of singlet fission (SF, eqn 2), [10][11][12][13][14][15][16] the reverse of TTA, have been…”