The π−π Stacked Geometries and Association Thermodynamics of Quinacridone Derivatives Studied by ¹H NMR

Abstract

The pi-pi stacked associations of three N,N'-di(n-butyl) quinacridone derivatives, widely used dopants in organic light-emitting diodes, with different sizes of substituents were investigated in solution at various temperatures by (1)H NMR spectroscopy. The pi-pi stacked geometries were estimated by both the magnitudes of peak shifts with concentration and the directions of peak shifts induced by polar solvents. Two patterns of geometries with different pi-pi interaction strengths were found to coexist in solution for all the three samples. In both of the patterns, the preferential orientation of the stacking is the approach of the carbonyl groups on one molecule to the nitrogen atoms on the stacked partner, which makes the pi-deficient aromatic atoms interact with both pi-rich and pi-deficient aromatic atoms of the stacked partner to maximize the electrostatic complementarity. Differently, whereas the molecules in one pattern are face-to-face stacked in a parallel fashion and slip two rings relative to one another along with the long axis of the conjugated ring systems, the molecules in the other are either face-to-face stacked in an antiparallel fashion with slight slipping between layers or stacked in a turning fashion. Both association constants obtained by fitting the dilution curves and thermodynamic parameters obtained from van't Hoff analyses revealed unexpectedly three thermodynamic processes of aggregations for all the three samples in the temperature region of 298-213 K. The size of substituents on the outer aromatic rings significantly influences the pi-pi stacked structures and association thermodynamics.

π–π interaction of quinacridone derivatives

“…48,49 We found that the geometries of the QA dimers are little affected by the lengths of the n-alkyl chains. To simplify calculation and save computational costs, we used different N,N 0 -dimethyl quinacridone derivatives as model molecules which are denoted as QA-C 1 , TM-QA-C 1 , DF-QA-C 1 , and DM-QA-C 1 (Fig.…”

“…We have previously studied the p-stacking geometries and association thermodynamics of N,N 0 -di(n-alkyl) quinacridone derivatives in solution by NMR. 48,49 The p-p interactions of N,N 0 -di(n-alkyl) quinacridone derivatives possessing larger p-conjugated units could offer stronger driving forces to compel molecules stacking as a faceto-face fashion in both crystal and solution structures, [48][49][50] which enable us to use these compounds as models to study the faceto-face interactions and get further understanding on the nature of p-p interactions. Moreover, both stacking manner and substituent property of quinacridone derivatives affect their luminescent color and charge transport property.…”

The structure‐dependent self‐association of five phenolic acids in aqueous solution

“…Different directions of the chemical shift displacements were also observed for chloroquine and quinacridone. [16,19] The upfield shifts demonstrated by aromatic ring A and aromatic ring C protons in the favored equiplanar geometry are commonly attributed to the strong interactions between the π systems, as in the case of several polyphenolic compounds. [10] The downfield shifts of the aromatic B and aromatic D ring protons may be attributable to the predominance of ring-current-induced diamagnetic deshielding effects from the opposing aromatic rings.…”

General statistical-thermodynamical treatment of one-dimensional multicomponent molecular hetero-assembly in solution

“…Non-covalent hetero-assembly of small molecules in solution is currently attracting great attention due to extensive use of this phenomenon in molecular electronics [1][2][3], laser physics [4,5], supramolecular chemistry [2,[6][7][8][9], advanced materials [10][11][12][13], numerous biochemical applications [2,14,15] etc. The key feature of this process is the formation of nanoscale aggregates, which modify the macroscopic physical properties of solute resulting in outcomes of practical importance ranging from discovering of new perspective materials to treatment of human diseases [16].…”