Fast Triplet Formation via Singlet Exciton Fission in a Covalent Perylenediimide-β-apocarotene Dyad Aggregate

Abstract

A covalent dyad was synthesized in which perylene-3,4,:9:10-bis(dicarboximide) (PDI) is linked to β-apocarotene (Car) using a biphenyl spacer. The dyad is monomeric in toluene and forms a solution aggregate in methylcyclohexane (MCH). Using femtosecond transient absorption (fsTA) spectroscopy, the monomeric dyad and its aggregates were studied both in solution and in thin films. In toluene, photoexcitation at 530 nm preferentially excites PDI, and the dyad undergoes charge separation in τ = 1.7 ps and recombination in τ = 1.6 ns. In MCH and in thin solid films, 530 nm excitation of the PDI-Car aggregate also results in charge transfer that competes with energy transfer from (1)*PDI to Car and with an additional process, rapid Car triplet formation in <50 ps. Car triplet formation is only observed in the aggregated PDI-Car dyad and is attributed to singlet exciton fission (SF) within the aggregated PDI, followed by rapid triplet energy transfer from (3)*PDI to the carotenoid. SF from β-apocarotene aggregation is ruled out by direct excitation of Car films at 414 nm, where no triplet formation is observed. Time-resolved electron paramagnetic resonance measurements on aggregated PDI-Car show the formation of (3)*Car with a spin-polarization pattern that rules out radical-pair intersystem crossing as the mechanism of triplet formation as well.

Solvent‐Dependent Singlet Fission in Diketopyrrolopyrrole Dimers: A Mediating Charge Transfer versus a Trapping Symmetry‐Breaking Charge Separation

“…[12,[19][20][21][22][23][24][25][26][27] Acenes, in general, and pentacenes in particular, fulfill all SF requirements and, consequently have attracted a great deal of attention. [16,24,[28][29][30][31][32][33][34][35] Other promising SF materials include rylene diimides [26,[36][37][38][39][40][41][42][43][44] and diketopyrrolopyrroles (DPPs). [45][46][47][48][49][50][51] Incentives for this study were to improve our understanding of intramolecular SF (i-SF) in DPP dimers.…”

“…The second is the indirect, two‐step mechanism, in which the population of the final 1 (T 1 T 1 ) is mediated by a transient state, either virtual or real. [ 12,19–27 ]…”

Understanding Ultrafast Dynamics of Conformation Specific Photo-Excitation: A Femtosecond Transient Absorption and Ultrafast Raman Loss Study

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] As compared to their inorganic analogues, they are relatively easy to synthesize at lower cost and they are gaining further attention because of their potential applications in nano scale physics. [20][21][22][23][24][25][26][27] A wide range of small organic molecules is currently under spectroscopic investigation by many groups. Examples of this class of molecules include linear pi-conjugated systems with acetylene bridges, ethyl bridges, phenyl bridges, heterocyclic aromatic bridges, etc.…”

Kontrolle des intramolekularen Förster‐Resonanzenergietransfers und der Singulettspaltung in einem Subporphyrazin‐Pentacen‐Konjugat mittels Lösungsmittelpolarität

“…charge transfer, CT). [12,[17][18][19][20][21][22][23][24][25][26] Dieser CT-Zwischenzustand kann entweder virtuell in Form eines Superaustauschmechanismus oder real sein, abhängig von seinem Energieniveau in Bezug auf die angeregten Singulett-und Tr iplettzustände.W elcher der beiden Mechanismen vorherrscht, hängt von Parametern wie elektronischer Kopplung, Orientierung der Chromophore usw.ab. Eine klare Richtlinie zur Vorhersage des Mechanismus wird bis heute noch diskutiert und untersucht.…”