Strengthening π–π Interactions While Suppressing C_sp2–H···π (T-Shaped) Interactions via Perfluoroalkylation: A Crystallographic and Computational Study That Supports the Beneficial Formation of 1-D π–π Stacked Aromatic Materials

Abstract

The design and synthesis of aromatic crystalline materials with controllable crystal structure packing is of particular interest in organic semiconductor and optoelectronic devices, where 1-D π−π stacked structures that enhance charge mobility are the most beneficial. We report here that the π−π interactions between aromatic molecules can be strengthened and the C sp2 −H···π (T−shape) interaction can be suppressed by perfluoroalkylation of corresponding aromatics. Both crystal structure data and ab initio calculations show that the π−π interaction is strengthened due to the electronic effects of perfluoroalkyl substituents, and the C sp2 −H···π interaction is suppressed by the steric effects of the perfluoroalkyl substituents. The C sp3 −F···F−C sp3 attractive interactions between perfluoroalkyl chains further stabilize the crystal structures. We also found that C sp3 −F···π interaction can be eliminated if an optimal electron deficiency of the π system is tuned by adjusting the number of perfluoroalkyl substituents. The insight gained from this study is of particular interest in organic semiconductor research as well as the fields of molecular recognition, sensing, and design of enzyme inhibitors where π−π interactions are also important.

PAH/PAH(CF3)n Donor/Acceptor Charge‐Transfer Complexes in Solution and in Solid‐State Co‐Crystals

“…This was not surprising because the individual structures of ANTH‐5‐1 and TRPH‐6‐1 contain stacks of molecules with π–π overlap similar to that for the acceptor pairs in ANTH/(ANTH‐5‐1) 2 and PYRN/(TRPH‐6‐1) 2 (see Figures S21 and S25) . Many structural investigations have shown that partial fluorination, trifluoromethylation, and or n ‐perfluoroalkylation tend to overcome herringbone crystal packing in PAH derivatives . Nevertheless, the structure of PYRN/(ANTH‐6‐1) 2 does not consist of stacks.…”

“…For example, R F substitution can raise the electron affinities (EAs) of polycyclic aromatic hydrocarbons (PAHs) by 0.3-0.5 eV per R F group [22,[24][25][26] and strengthen parallel p-p interactions whiles uppressing Tshaped CÀH···p interactions. [27][28] Fluorination,even partial fluorination, can also increaseP AH electron affinities, [29][30] improve air stability, [24,31,32] affect PAHc hargem obility [33] and photophysics, [34] convert p-type into n-type semiconductors [24,31,32,35] (e.g.,p erfluoropentacene [31,35] ), and convert PAH herringbone structures (e.g.,a nthracene (ANTH) [36] )i nto pstacked structures (e.g.,1 ,2,3,4-ANTH(F) 4 [37] ). [38,39] However,C F 3 is am uch stronger electron-withdrawing group (EWG) than F. [22,40,41] For example, the DFT-predicted EAso fp erfluoroanthracene (ANTH(F) 10 )a nd ANTH(CF 3 ) 10 are 1.84 [29,30] and 4.01 eV, [24] respectively.W ith only six CF 3 groups,t he experimental EA of 2,3,6,7,9,10-ANTH(CF 3 ) 6 (ANTH-6-1), at 2.81(2) eV, [26] is more than 1eVh ighert han ANTH(F) 10 and is the same as the 2.78 (6) eV EA of the common charge-transfer electron acceptor chloranil (2,3,4,5-tetrachlorobenzoquinone; Cl 4 BQ).…”

Metal–organic coordination polymers based on Cs(I), Rb(I) and isoflavone-3′-sulfonate ligands

“…At the same time, the coordination interactions between Cs + and O atoms link the neighboring Cs into an infinite Cs-O-Cs chain along b axis. In 1 and 2, all the stacking distances indicate the existence of aromatic stacking interactions [47,48].…”

Molecular insights into photostability of fluorinated organic photovoltaic blends: role of fullerene electron affinity and donor–acceptor miscibility

“…5,[34][35][36][37][38] Fluorine substitution into the polymer backbone has been shown to impart a number of benecial effects on the material as an OPV donor: strategic uorination can (i) increase polymer crystallinity, 39 which in turn can improve both charge mobility 40 and photostability; 41 (ii) tune the optoelectronic properties of the donor material; 42 and (iii) strongly inuence dipole moments in the material that in turn affect charge separation and recombination. 43 Specic uorine interactions can also have a strong inuence on the solid-state morphology of active layer blends, 4,38,[44][45][46] and they have recently been employed by our group to inuence long-range structural order in other organic conjugated systems such as covalent organic frameworks. 47 For this work, we focused our efforts on several high performance OPV polymers and their structural analogues, shown in Fig.…”