Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - CyclAr (Cyclic Arylenevinylene Polymers)

Teaser

This project was directed towards solving some of the crucial problems associated with the usage of linear conjugated polymers with end groups in electronic applications such as organic photovoltaics (OPVs), organic field effect transistors (OFETs) and organic light emitting...

Summary

This project was directed towards solving some of the crucial problems associated with the usage of linear conjugated polymers with end groups in electronic applications such as organic photovoltaics (OPVs), organic field effect transistors (OFETs) and organic light emitting diodes (OLEDs). Even though the physical and optoelectronic properties of most of the linear conjugated polymers are in the desirable range for electronic applications the performance is not up to the expected level. This is partially due to the presence of end groups that can act as charge traps and source for degradation pathways resulting in poor device performance. Through this project we tried to address this issue by proposing cyclic conjugated polymers without end groups which can potentially exhibit better performance than the linear polymers due to lack of end groups. Also, a novel catalytic method was developed for the preparation these cyclic conjugated polymers.

Development of high performing conjugated polymers for electronic applications is an essential area of research for technological advancement of the society. The cyclic polymers with optimal optoelectronic will be used as active layer in OPVs, OFETs and OLEDs for light harvesting, sensor applications and display technology respectively.

The main objective of this project was to develop efficient synthetic methods to prepare novel conjugated cyclic polymers to address the limitations of their linear congeners. The overall objectives of this project were to design and synthesis of novel polymeric structures, studying their physical, optical and electrochemical properties. Eventually, testing performance of these novel materials in device fabrication.

In order to achieve these objectives novel catalytic polymerisation methods were developed for the preparation of fully conjugated cyclic polymers (p-arylenevinylene polymers) and novel polymeric topologies. In addition, some of these methods were used to prepare poly(p-arylenevinylene) block copolymers.

Work performed

Developing high performing conjugated polymers for electronic applications is an important research. Our efforts were directed towards the synthesis and polymerisation of novel electron rich and electron deficient paracyclophane-1,9-diene monomers to achieve cyclic polymers with various topologies. Along these lines five novel cyclophanediene monomers were synthesised and polymerisation of some of these was studied using ruthenium carbene initiators. A ring-expansion metathesis polymerisation (REMP) of strained paracyclophanediene monomers was developed using cyclic ruthenium carbene catalysts to obtain fully conjugated cyclic polymers. Also, photophysical studies on these systems were performed to differentiate from their linear congeners.

Towards achieving the synthesis of cyclic polymers with novel topologies (trefoil, 8-shape and donor-acceptor rings) a bidirectional ring-opening metathesis polymerisation (BDROMP) of paracyclophanediene monomers was developed. These polymerization reactions were end capped efficiently using various vinyl ethers to obtain polymers with cationic and anionic end groups. A covalent fixation by electrostatic self-assembly methodology will be used to obtain these topologies. In addition, a powerful application of this BDROMP methodology was realised in the synthesis of tri and pentablock copolymers via sequential ROMP of two different monomers. Also studied optical and electrochemical properties of these block copolymers.

A completed piece of this work was published in a renowned scientific journal (Chemical Science) and important findings of the project were communicated through oral presentations in international conferences such ACS meetings and Macro18 polymer congress held in this year in USA and in Australia respectively.

• “Macrocyclic Poly(p-phenylenevinylene)s by Ring Expansion Metathesis Polymerisation and their Characterization by Single-Molecule Spectroscopy” B. J. Lidster, S. Hirata, S. Matsuda, T. Yamamoto, V. Komanduri, D. R. Kumar, Y. Tezuka, M. Vacha, M. L. Turner, Chem. Sci., 2018, 9, 2934-2941 (DOI: 10.1039/c7sc03945j).

• “An Unprecedented Bidirectional ROMP of Strained Paracyclophane1,9-dienes to Tri and Penta Conjugated p-Phenylenevinylene Block Copolymers” V. Komanduri, D. R. Kumar, D. Tate, R. M. Hernandez, B. J. Lidster, M. L. Turner, Manuscript in preparation.


• “Synthesis of Phenyl-Benzothiadiazolevinylene Donor-Acceptor Block coPolymers via Ring-Opening Metathesis Polymerisation of 1,9-Paracyclophanedienes” V. Komanduri, D. Tate, R. M. Hernandez, D. R. Kumar, M. L. Turner, Manuscript in preparation.

Final results

Having realised the advantages of cyclic conjugated polymers over the linear polymers with end groups for electronic applications many research groups around the world have been investigating efficient synthetic methods for the preparation of these targets. However, there are only very few efficient synthetic methods that came out of these efforts. For the first time we achieved synthesis of fully conjugated macrocyclic (p-phenylenevinylene)s via REMP of strained cyclophanediene monomers in a controlled fashion. Also, a bidirectional ROMP of cyclophanediene monomers towards the synthesis of achieving various topologies is very novel. In addition, the ROMP methods developed in our laboratory were showcased in the synthesis of tri, pentablock copolymers and donor-acceptor block copolymers which otherwise are difficult to access in a controlled way via existing methods, this is a very good contribution to the field (scientific impact).

A bidirectional ROMP followed by covalent fixation is an elegant strategy proposed to obtain novel topologies especially donor-acceptor rings connected by a covalent linkage. Photophysical studies on these systems can shine light on some of the important aspects of charge separation in light harvesting. Thus the efforts on development of novel conjugated polymers for solar cell applications can contribute to the Solar Europe Industry Initiative (SEII) implementation plan for 2020 that intends to meet 12% of supply of European electricity demand through photovoltaics. The supply of electricity through photovoltaics projected to reach 20% by 2030 (socio-economic impact).

In addition, through this training the researcher Dr. Komanduri developed necessary skills to become an independent researcher and lead his own research group. Also, through his visits to international conferences Dr. Komanduri established contacts with renowned scientists in the field for future explorations and collaborations (Impact on researcher’s career).

Website & more info

More info: http://www.functionalmaterials.org.uk.