Efficient Free Triplet Generation Follows Singlet Fission in Diketopyrrolopyrrole Polymorphs with Goldilocks Coupling

Abstract

Microcrystal electron diffraction, grazing incidence wideangle scattering, and UV−vis spectroscopy were used to determine the unit-cell structure and the relative composition of dimethylated diketopyrrolopyrrole H-and J-polymorphs within thin films subjected to vapor solvent annealing (VSA) for different times. The electronic structure and excited-state deactivation pathways of the different polymorphs were examined by transient absorption spectroscopy, conductive probe atomic force microscopy, and molecular modeling. We find that VSA initially converts amorphous films into mixtures of H-and J-polymorphs and promotes further conversion from H to J with longer VSA times. Though both polymorphs exhibit efficient SF to form coupled triplets, free triplet yields are higher in J-polymorph films compared to mixed films because coupling in J-aggregates is lower and, in turn, more favorable for triplet decoupling.

Excimer Formation Inhibits the Intramolecular Singlet Fission Dynamics: Systematic Tilting of Pentacene Dimers by Linking Positions

“…In order to perform an efficient SF process in the compound, the requirements of energy, possessing E (S 1 ) ≥ 2E (T 1 ) along with E (T 2 ) ≥ E (S 1 ), and geometry, having appropriate interchromophore electronic coupling, have to be satisfied. ,,, There are two widely accepted mechanisms through which SF occurs: a two-electron process that directly converts the initial 1 (S 1 S 0 ) state into the correlated triplet pair state 1 (T 1 ···T 1 ) and another one mediated through a coupling of a higher-lying charge transfer state by two consecutive one-electron processes converting 1 (S 1 S 0 ) to 1 (T 1 ···T 1 ). , It is found that the formation of excimers or excimer type states controlled the efficiency and dynamics of the SF process where excimers possessed both the character of singlet and triplet states as well as the charge transfer state. , However, the fundamental understanding of the underlying mechanism is not clear due to the complexity of the interactions as well as nature of the 1 (S 1 S 0 ) and 1 (T 1 ···T 1 ) states by the electronic coupling between the chromophores affected by the configuration of the structures. ,,, The significance of the structural heterogeneity, controlling the efficiency of singlet fission dynamics by the change of the electronic coupling due to conformational flexibility, was investigated in detail. − There was the evidence of formation of excimers as an intermediate either to prevent − or enhance the iSF process. The excited-state relaxation pathways of various types of polyaromatic dimers have been investigated to understand the importance of the excimer formation during the iSF process. ,− …”

Electron Diffraction of 3D Molecular Crystals

“…If this “shake-n-bake” method produces an unduly sparse distribution of crystals, an alternative strategy involves immersing a small quantity of powder in a volatile solvent (ideally one in which the substrate is completely insoluble), drop-casting 2–3 μL of the resultant slurry directly onto the grid using a micropipette, and allowing it to air-dry at RT. Alternatively, crystals suitable for ED can be grown or annealed directly on EM grids by drop-casting a dilute solution of analyte and letting it evaporate, prompting in situ nucleation and crystallization. , Optionally, excess solvent can be wicked away using filter paper or drained under reduced pressure by a vacuum pump . Because the amorphous carbon surface of many grids is somewhat hydrophobic, it generally interferes with adherence of aqueous solvents.…”

“…Alternatively, crystals suitable for ED can be grown or annealed directly on EM grids by drop-casting a dilute solution of analyte and letting it evaporate, prompting in situ nucleation and crystallization. 54,55 Optionally, excess solvent can be wicked away using filter paper or drained under reduced pressure by a vacuum pump. 56 Because the amorphous carbon surface of many grids is somewhat hydrophobic, it generally interferes with adherence of aqueous solvents.…”

Complete Set of Diketopyrrolopyrrole Centrosymmetrical Cofacial Stacked Pairs

“…264, file XODFAX in the Cambridge Crystallographic Data Centre (CCDC) database [17d] ), are excluded. We also do not consider C 2 stacks as found, for example, for a polymorph of N , N' ‐dimethylated ThDPP , [14d] and C i stacks in which only the rings at the 3 , 6 ‐positions of the DPP participate, which are found for some DPPs with extended 3 , 6 ‐substituents containing condensed rings, such as benzothiophene substituents (CCDC file KEMDAJ [13c] ) and the thienothiophene analogue of 2 ‐ethylhexylated ThDPP (file SIGFUM [13f] ) or alkylated bithiophene (file FACPUY [13h] ). Stacks of extended DPPs, in which DPP rings overlap with rings other than the closest ring, as in benzofuranyl‐substituted ThDPP (file KEMDIR02 [13c] ), are also not considered.…”