Singlet Fission via an Excimer-Like Intermediate in 3,6-Bis(thiophen-2-yl)diketopyrrolopyrrole Derivatives

Abstract

Singlet fission (SF) in polycrystalline thin films of four 3,6-bis(thiophen-2-yl)diketopyrrolopyrrole (TDPP) chromophores with methyl (Me), n-hexyl (C6), triethylene glycol (TEG), and 2-ethylhexyl (EH) substituents at the 2,5-positions is found to involve an intermediate excimer-like state. The four different substituents yield four distinct intermolecular packing geometries, resulting in variable intermolecular charge transfer (CT) interactions in the solid. SF from the excimer state of Me, C6, TEG, and EH takes place in τSF = 22, 336, 195, and 1200 ps, respectively, to give triplet yields of 200%, 110%, 110%, and 70%, respectively. The transient spectra of the excimer-like state and its energetic proximity to the lowest excited singlet state in these derivatives suggests that this state may be the multiexciton (1)(T1T1) state that precedes formation of the uncorrelated triplet excitons. The excimer decay rates correlate well with the SF efficiencies and the degree of intermolecular donor-acceptor interactions resulting from π-stacking of the thiophene donor of one molecule with the DPP core acceptor in another molecule as observed in the crystal structures. Such interactions are found to also increase with the SF coupling energies, as calculated for each derivative. These structural and spectroscopic studies afford a better understanding of the electronic interactions that enhance SF in chromophores having strong intra- and intermolecular CT character.

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

“…[3][4][5][6][7] On the other hand it has been recently found that excimer formation can also have a positive effect on the properties of organic materials, facilitating processes such as singlet fission. [8][9][10][11][12] For this reason, the understanding of the excimer formation dynamics in molecular aggregates is of fundamental importance for the development of novel materials that can be employed in organic electronics or photovoltaics applications. In addition to their importance for the development of functional materials, excimers can be also employed as probes in biological molecules.…”

Machine Learning for Understanding the Relationship between the Charge Transport Mobility and Electronic Energy Levels for n‐Type Organic Field‐Effect Transistors

“…The development of solution-processable OFETs has attracted great interest because of its cost-effective and low-energy consumption processes. [9,10] www.advelectronicmat.de gold-based p-type OFETs would perform much better than goldbased n-type OFETs, for example, having high mobility values, due to relatively small energy barriers between Au and p-type active layer. OFETs based on p-type organic semiconductors and gold source/drain electrodes achieved much progress during the last two decades.…”

Liquid Crystallinity as a Self‐Assembly Motif for High‐Efficiency, Solution‐Processed, Solid‐State Singlet Fission Materials

“…HBC is a polycyclic aromatic hydrocarbon made up of thirteen fused six membered rings, which forms a mesophase. [6,37] Their studies on substituent variation in crystalline diketopyrrolopyrroles demonstrated that the torsion induced on substitution of thienyl (TDPP) by phenyl (PDPP) is sufficient to increase the π-π stacking distance and completely shut down SF, so SF in DPP is very sensitive to local-order (intermolecular coupling), which is not ideal for inclusion in OPV devices. [35] The HBC core shows strong π−π intermolecular association and can show high charge mobilities (≈1 cm 2 V −1 s −1 in certain silyl-substituted HBCs using pulse-radiolysis time resolved microwave conductivity measurements).…”

“…Soluble HBC derivatives show strong self-association in solution and discotic columnar structures with ordered morphology in films. [37] Our interest in developing solution processable SF materials for use for printed organic solar cells, led us to question, can we use the liquid crystallinity inherent in FHBC as a self-organizing motif and scaffold to pre-organize the DPP chromophore to promote intramole cular SF in amorphous thin films? [36] Substitution of HBC with 9,9-dioctylfluorene (FHBC) imparts solubility and the ability to form mixtures with other conjugated molecules.…”