Structure and photophysics of indigoids for singlet fission: Cibalackrot

Abstract

We report an investigation of structure and photophysics of thin layers of cibalackrot, a sturdy

Singlet Fission in Thin Solid Films of Bis(thienyl)diketopyrrolopyrroles

“…The approximations make the calculations so fast that it is easily possible to search the entire 6‐dimensional space of all possible molecular pair configurations using a grid of billions of geometries, and to identify all local maxima of the SF rate. Testing at about a hundred geometries showed that the results correlated well with those obtained at a good ab initio level, both for ethylene [18] used as a model, and for cibalackrot [20] …”

“…Still, regardless of the method of preparation and the solid chosen, But‐ 1 , Hex‐ 1 , or Ada‐ 1 , the spectra of the solids resemble the solution spectra sufficiently to instill confidence that similar assignments apply in the three cases, and that they can be discussed together. Although the dominant transitions from S 0 and T 1 do not have parallel polarizations, they do not require corrections for the effects of molecular orientation [20] when they are used for quantitation of the relative abundancies of these two states, because the samples show nearly isotropic absorbance.…”

“…The same angular deviations occur in the slip‐stacked molecular pairs found in the crystal structure of the But‐ 1 SC film. The absence of coincidence of the directions of the moments of the T 1 ‐T 5 and S 0 ‐S 1 transitions, used to monitor the concentrations of triplet and singlet excitons, respectively, opens the possibility that corrections for partial molecular alignment in our samples might be needed, [20] but this need is ruled out by the optical isotropy that is observed in spite of indications from X‐ray diffraction that some supramolecular organization relative to the substrate surface is present. The absence of coincidence of the slip vector with the direction of the S 0 ‐S 1 (HOMO‐LUMO) transition dipole moment means that the anticipated effect of the slip on the SF matrix element is reduced, since only the projection of the slip vector into this direction matters.…”

“…[45][46][47] All quantum-chemical calculations used the Gaussian program package. [48] Screening of the pair geometries: For computation of SF rate constants at geometries found in crystals and for identification of molecular pair geometries that optimize the rate of SF, we used the freely available computer program SIMPLE, described elsewhere [18][19][20] (a thorough description of an older version is also available). [6,11] Within a range of intermolecular distances specified, it identifies all local maxima of the SF rate constant k SF for conversion of a singlet exciton to a biexciton as a function of molecular pair geometry (six degrees of freedom), avoiding molecular interpenetration using the hard-sphere model.…”

Strategies for Design of Potential Singlet Fission Chromophores Utilizing a Combination of Ground State and Excited State Aromaticity Rules

“…38,39 Now, what are the explicit scopes of T 1 -state Bairdaromaticity for the design of singlet fission chromophores, and what are the limitations? It was argued by Ryerson et al, 40 when analyzing the INDT compounds by Fallon et al, 37 that the intermediate triplet-state aromaticity yielding the E(S 1 ) = 2E(T 1 ) situation needs to be found through inspection of calculated adiabatic excitation energies. Thus, a qualitative tool should be desirable.…”