title: Nanostructured donor-acceptor self assembly with improved photoconductivity.
abstract: Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)]1.0 upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (∼500 nm) and PBI (∼640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (∼430 nm) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 nm. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)]1.0 exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly.
authors.affiliation: Polymer Science and Engineering Division, ‡Catalysis & Inorganic Chemistry Division, CSIR-National Chemical Laboratory , Dr. Homi Bhabha Road, Pune 411008, India.
authors.forename: B
authors.initials: B
authors.lastname: Saibal
authors.forename: A Z
authors.initials: AZ
authors.lastname: Ashar
authors.forename: R Nandini
authors.initials: RN
authors.lastname: Devi
authors.forename: K S
authors.initials: KS
authors.lastname: Narayan
authors.forename: S K
authors.initials: SK
authors.lastname: Asha
keywords: donor−acceptor; hydrogen bonding; oligo(p-phenylenevinylene); perylenebisimide; photoconductivity; supramolecular polymeric nanostructures