ARTICLE OBC www.rsc.org/obc The design and synthesis of porphyrin/oligiothiophene hybrid monomers Gavin E. Collis, a Wayne M. Campbell, b David L. Officer* b and Anthony K. Burrell* a a Actinide, Catalysis and Separations Chemistry, C-SIC, Mail Stop J514, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA. E-mail: Burrell@lanl.gov; Fax: 505 667-9905; Tel: 505 667-9342 b Nanomaterials Research Centre – Massey University, Private Bag 11222, Palmerston North, New Zealand. E-mail: D.Officer@massey.ac.nz; Fax: 64 6 350-5682; Tel: 64 6 356-9099 Received 21st February 2005, Accepted 29th March 2005 First published as an Advance Article on the web 29th April 2005 In an effort to build effective photovoltaic cells based on porphyrin-functionalised polythiophenes we have focused on synthetic routes to three monomer types. By controlling the geometric structure of the monomer, oxidation of these materials should produce polymers with different architectural structures, and as a result, different opto-electronic properties. Employing Wittig protocols allowed access to monomers in which the porphyrin moiety is connected to the b-position of the thiophene via an alkene linkage. In addition, monomers were constructed using porphyrin condensation methods to afford a-thiophene meso-substituted porphryins. Another set of monomers was also prepared via porphyrin condensation routes, but instead utilising b-formylthiophenes. By utilising different formyloligothiophenes we were able to generate a series of monomers that can be used to control the loading of the porphyrin in the polythiophene matrix. Introduction Since their discovery, Inherently Conducting Polymers (ICPs) have held a special place in material science. The ability to design organic polymers that exhibit desirable electronic and opto- electronic properties has resulted in an explosion of applications, e.g. LEDs, electrochromics, photovoltaics, electrocatalysis and sensor devices. 1 In particular, these polymers have been used to develop hybrid materials that, when combined, optimise the properties of the individual components or, ideally, have properties that outweigh the sum of the parts – i.e. “synergic materials”. 2 In recent years, significant interest has focused on using hybrid materials in photovoltaic devices as an alternative to silicon-based technology. One approach has been to use an organic component, such as a dye, and an inorganic component, such as a conductive metal-based film. To date, the most commercially advanced hybrid photocell device of this type is the Gratzel ruthenium-bipyridyl/TiO 2 /liquid electrolyte cell. 3 However, there is still a need to minimise fabrication costs, reduce construction complexity and to increase photoenergy conversion in photocells. In theory, this can be achieved by op- timising the key components of a photocell, such as the charac- teristics of the metal oxide surface, the effectiveness of the light- capturing system and the charge separation/transportation processes. 4 One such area of interest has been solid-state solar cells designed from conducting polythiophenes that incorpo- rate light-harvesting systems. For instance, photocurrents have been obtained from polymers derived from oligothiophenes axially coordinated to phosphorous-centred porphyrins, 5 from fullerenes grafted onto the backbone of polythiophene 6 and, more recently, from ordered polythiophenes that contain sim- ple organic donor and/or acceptor groups, 7 or from mixed porphyrin–acetylene–thiophene copolymers. 8 Our group has previously been concerned with the synthesis and study of porphyrins as artificial light harvesters, 9 and, more recently, in making new functionalised conducting polymers from terthiophene monomers. 10 Combining these two areas of research, we were intrigued as to how the opto-electronic properties of the photocell could be improved by manipulating the molecular architecture of the porphyrin/thiophene polymer deposited on the metal oxide surface. Structural order at a molecular level, in part, can be imprinted by the design of the monomeric unit. 11 A number of approaches can be taken to this, as shown by Fig. 1. Types I–III are similar in that the porphyrin unit is covalently attached to the b-position of the polymer backbone. Type I polymers, where the porphyrin is attached to the thiophene backbone via an alkyl linker, have been synthesised and studied for electrocatalysis and for use in sensor devices. 12 However, in these hybrid systems, the polymer Fig. 1 Graphical representation of Type I–V polymer structures. DOI: 10.1039/b502517f This journal is © The Royal Society of Chemistry 2005 Org. Biomol. Chem. , 2005, 3 , 2075–2084 2075 Published on 29 April 2005. Downloaded by CSIRO Library Services on 20/04/2015 03:02:59. View Article Online / Journal Homepage / Table of Contents for this issue