Structure–Property Relationships in Bithiophenes with Hydrogen‐Bonded Substituents

Abstract

The use of crystal engineering to control the supramolecular arrangement of π‐conjugated molecules in the solid‐state is of considerable interest for the development of novel organic electronic materials. In this study, we investigated the effect of combining of two types of supramolecular interaction with different geometric requirements, amide hydrogen bonding and π‐interactions, on the π‐overlap between calamitic π‐conjugated cores. To this end, we prepared two series of bithiophene diesters and diamides with methylene, ethylene, or propylene spacers between the bithiophene core and the functional groups in their terminal substituents. The hydrogen‐bonded bithiophene diamides showed significantly denser packing of the bithiophene cores than the diesters and other known α,ω‐disubstituted bithiophenes. The bithiophene packing density reach a maximum in the bithiophene diamide with an ethylene spacer, which had the smallest longitudinal bithiophene displacement and infinite 1D arrays of electronically conjugated, parallel, and almost linear N−H⋅⋅⋅O=C hydrogen bonds. The synergistic hydrogen bonding and π‐interactions were attributed to the favorable conformation mechanics of the ethylene spacer and resulted in H‐type spectroscopic aggregates in solid‐state absorption spectroscopy. These results demonstrate that the optoelectronic properties of π‐conjugated materials in the solid‐state may be tailored systematically by side‐chain engineering, and hence that this approach has significant potential for the design of organic and polymer semiconductors.

High-throughput virtual screening for organic electronics: a comparative study of alternative strategies

“…Hopping transport theory, despite being not fully applicable to molecular semiconductors, due to its simplicity and low computational cost, remains a frequent method of choice in the majority of HTVS studies, including those using large databases, [269][270][271] as well as those evaluating smaller libraries of structures. [272][273][274][275] Applying this theory to screen the CSD, as the world's largest repository of small organic/metal-organic molecules whose crystalline structures are experimentally known, 186 C. Schober et al made an important contribution demonstrating, for the first time, that large scale screening of materials for transport applications is possible. 269 The transfer integral and the reorganisation energy are the main components of the hopping transport theory.…”

Engineering polymers with improved charge transport properties from bithiophene-containing polyamides

“…The detailed synthesis conditions for 3,3'-(2,2'-bithiophene-5,5'-diyl)dibutyric acid (T2) and dipropyl 4,4'-(2,2'-bithiophene-5,5'-diyl)dibutanamide (T2a) have been reported elsewhere. 24 NMR Spectroscopy. NMR spectroscopy was performed on a Bruker Avance III 400 spectrometer at 400 MHz and 100 MHz magnetic field strength at 298 K for 1 H and 13 C nuclei, respectively.…”

“…The required tilt of the amide groups is nevertheless small, resulting in monoclinic packing and a centered unit cell in which the overall chain conformations remain close to the all-trans conformations characteristic of the α phase. 41 To model the molecular arrangement of the polyamides PAnT2, and specifically the packing behavior of the bithiophene unit, we used the single-crystal X-ray structure of model compound T2a as a starting point, 24 because its solid-state IR spectra showed very similar features (Figure 2a Trial crystal structures for PAnT2 with even n (Figure 4a) were hence generated assuming a triclinic unit cell, packing and conformations analogous to those observed for T2a, and an all-trans conformation for the aliphatic segments, consistent with the solid-state IR spectra. For convenience, the c axis of the unit cell was chosen to be parallel to the axis of the aliphatic sub-chains, so that changes in n could be accommodated by adjusting c. In the case of n = 8, the unit cell parameters were adjusted to fit the peak positions from selected-area electron diffraction (SAED) patterns from oriented friction deposited films (Figure 4b), in which the higher order peaks were well resolved and the layer line spacing provided an estimate of the c repeat distance along the orientation axis.…”

Structure–Assembly–Property Relationships of Simple Ditopic Hydrogen-Bonding-Capable π-Conjugated Oligomers

“…[23][24][25][26][27][28] Our interest in HB units extends from our attempts to program bulk heterojunction photovoltaic active layer structures in vacuum-deposited films. [29][30][31] We have gravitated towards rosette-forming HB units because our earlier work showed these can confer columnar supramolecular architectures upon π-stacking that facilitate charge transport and blend well with fullerenes in the context of bulk heterojunction OPV active layers. 24,32 Our initial studies focused on "monotopic" designs, wherein a HB-capable unit was appended on only one terminus of a mostly linear π-conjugated system (Figure 1a).…”