Conversion of Face‐On Orientation to Edge‐On/Flat‐On in Induced‐Crystallization of Poly(3‐hexylthiophene) via Functionalization/Grafting of Reduced Graphene Oxide with Thiophene Adducts

Abstract

Reduced graphene oxide (rGO) is functionalized with 2-thiophene acetic acid (rGO-f-TAA) and grafted with poly(3-dodecylthiophene) (rGO-g-PDDT) and poly(3-thiophene ethanol) (rGO-g-PTEt) to manipulate the orientation and patterning of crystallized poly(3-hexylthiophene) (P3HT). P3HT chains prefer to interact with their thiophene rings with bared rGO surface, resulting in a conventional face-on orientation. In these hybrids, beyond critical length of P3HT nanofibers developed onto rGO (>100 nm), an inclination occurs after solvent evaporation, thereby face-on noninclined fibers change to edge-on inclined ones. In P3HT/rGO-f-TAA supramolecular structures patterned with P3HT short nanofibrils (42-95 nm in length), the orientation of P3HT chains changes from face-on to edge-on, originating from strong interactions between hexyl side chains of P3HTs and 2-thiophene acetic acid functional groups of rGO. Supramolecular structures based on grafted rGO demonstrate a patched-like morphology composed of flat-on P3HTs with main backbones perpendicular to substrate. Grafted polythiophenic oligomers onto rGO (rGO-g-PDDT and rGO-g-PTEt) provoke P3HT backbones to vertically attach to surface and remain perpendicular even after solvent evaporation. Flat-on orientation acquired for rGO-g-PDDT and rGO-g-PTEt systems is the best for P3HT chains assembled onto rGO. Face-on P3HT/rGO hybrids and, subsequently, edge-on P3HT/rGO-f-TAA hybrids also reflect optical and supramolecular donor-acceptor properties based on ultraviolet-visible and photoluminescence analyses.

Novel conjugated patterns of PBDT‐DTNT and PBDT‐TIPS‐DTNT‐DT complicated polymers onto graphenic nanosheets

“…In this work, the surfaces of rGO nanosheets were patterned via assembling the PBDT‐DTNT and PBDT‐TIPS‐DTNT‐DT complicated conductive polymers. In spite of distinct orientations and configurations previously detected for the P3HT crystallization onto the bare, functionalized and grafted rGO nanosheets, herein, only the conductive patternings were manipulated via surface modification. The polymer chains encountered a considerable hindrance while assembling onto the grafted rGO nanosheets, thereby some delicate and limited patterns were allowed to be developed.…”

“…Hole transporter‐functionalized rGO and graphene–fullerene composite have also been reported in the literature. Very recently, the orientation of P3HT chains has also been manipulated onto rGO nanosheets through functionalization and grafting of the nanosheet surface …”

Crystallization of D-A Conjugated Polymers: A Review of Recent Research

“…According to which crystal axis is perpendicular to the substrate, the molecular orientation of conjugated polymers could be divided into three types: face-on, edge-on and flat-on. In films, conjugated polymers generally adopt a face-on or edge-on orientation [121,122]. If the π-π stacking direction is perpendicular to the substrate, the molecular orientation is named "face-on".…”

Crystal Structure Control of the Energetics of Chemical Doping in Rub-Aligned P3HT Films

“…P3HT crystallites have a monoclinic unit cell with side chains that are tipped away from the aromatic ring plane to better fill space . When cast as a thin film, P3HT has been shown to form both edge-on (i.e., alkyl side chains contacting the substrate) and face-on (i.e., backbone rings contacting the substrate) crystallites depending on the processing conditions and substrate interfacial energy. − Although as-deposited semiconducting polymer films are typically isotropic with regard to the in-plane rotational angle (φ), there are a number of methods for aligning crystallites within the film, which range from strain-based or float-casting methods to the use of textured substrates. ,− Work by Brinkmann and co-workers produced aligned P3HT films by rub-alignment, resulting in highly crystalline and aligned polymers. These researchers used electron diffraction (ED) to show that the rub-aligned films have both face-on- and edge-on-oriented P3HT polymorphs. ,,− In subsequent studies, they also used aligned films to better understand how the P3HT crystal structure changed upon doping.…”