Complete Set of Diketopyrrolopyrrole Centrosymmetrical Cofacial Stacked Pairs

Abstract

Stacked centrosymmetrical dimers and simultaneously H‐bonded and stacked hexamers of thiophene‐substituted diketopyrrolopyrrole (ThDPP) were studied using DFT as models for crystals with slipped‐stacked molecules in 1D columns. Eight stacked dimer arrangements were found, six of which are driven by the minimisation of electron repulsion and realised by placing the partially negatively charged atoms of the diketopyrrolopyrrole rings below the centre of an adjacent thiophene ring. Four of these stacks are related to N,N'‐dialkylated derivatives of ThDPP found in the literature, while a further one is related to an N,N'‐diacylated derivative. An analogous set of eight stacks was discovered computationally for phenyl‐substituted DPP (PhDPP), four of which are known among H‐bonded DPP pigments, and one more among N,N'‐dialkylated PhDPP derivatives. The results shed more light on the mechanisms that drive the formation of stacks between nonaromatic (DPP) and aromatic (Th, Ph) rings. The excitation energies of the lowest four singlet states computed by TD DFT enabled excitonic coupling and energy separation between Frenkel‐resonance‐type and charge‐transfer states to be established, depending on the equilibrium stack geometry.

Four Slip‐Stacked Arrangements, Three Types of Photophysics: Crystal Structure and Solid‐State Fluorescence of 3,6‐Diaryl Substituted Furo[3,4‐c]furanone Polymorphs and Regioisomers

“…Lower binding energy of dimer 6, compared to the dimers 1, 3 and 5 (Table 1), and its inability to form a self-standing minimum in a dimer approximation explain, that's why this π-stack arrangement needs a significant support of further specific interactions (CO-HC, CH-π and COÀ O) to be stabilized, i. e. to avoid a slip to the more stable arrangement. In fact, this is only the second report on a detection of this rare type of packing within DFF/DPP family [15,19] . On the other hand, stacking in dimer 1, 3 or 5 fashion is quite common between DPPs, e.g for P.R.…”

“…Geometrical characteristics and binding energies are summarized in Table 1. All dimer geometries on Figure 5 and in Table 1 come from central dimers extracted from optimized 3x2 hexamers, in which three molecules in each layer (Figure S1) were fixed by C=O attraction to phenyl hydrogens either in positions 2 and 3 (dimers 1 – 7 ) or 3 and 4 (dimer 8 ), formally substituting the natural CO−NH in‐layer hydrogen bonds used for modelling of DPP pigments [15] . Only dimers 1 – 5 could be obtained by dimer optimization of 3 a , while for meta tetramethylated 3 f (and for the less probable rotamer, than observed in crystal of 3 c ) also a minimum, relating to dimer 6 , was computed.…”

“…Quantum chemical calculations found the same set of eight possible centrosymmetrical slipped π-stacks of 3 a (Figure 5) as for PhDPP. [15] Geometrical characteristics and binding energies are summarized in Table 1. All dimer geometries on Figure 5 and in Table 1 come from central dimers extracted from [33] ) and 3 e (down).…”

“…[49] The resulting geometries were characterized by planeto-plane (PP) and centre-to-centre (CC) distances between DFF cores of both monomers in a dimer. [15] Computed PP and CC were evaluated by Mercury 3.9. [50] Excitation energies of the lowest six singlet states of the dimers were computed by TD DFT with ωB97X-D [51] xc functional and 6-311 + G(2d,p) basis set.…”

“…Thus, among eight possible centrosymmetrical π-stacked arrangements in 1D infinite columns of diketopyrrolopyrroles, the only one and, furthermore, relatively less stable, should show J-type photophysics. [15] Altogether, observing intense SSF in polycrystalline materials with infinite homogenous columns, formed by H-type π-stacks, is uncommon.…”