Cardiff University Cardiff School of Chemistry Synthesis and characterization of borazine -doped polyphenylenes: towards the construction of boron -nitrogen - carbon hybr id polycyclic aromatic hydrocarb ons Davide MARINELLI PhD Thesis December 2017 Supervisor: Prof. Dr. Davide BONIFAZI Doctoral commission: Prof. Emilio M. Pérez Dr. Louis Morrill Acknowledgements First of all, I would like to thank Professor Bonifazi , my supervisor. I am very grateful to him for his constant support and help. Nonetheless, thanks to him I had the possibility to travel and work in different countries , gathering all the best from the fantastic people I’ve met around Europe . I’d like to say a big thank you to Tanja , for the help she gave me during these years and for the revision of this manuscript. I am extremely grateful to the members of the borazine team: María , Jacopo, Francesco, Jack, Jonathan, and Hamid . Many thanks also to the rest of the group members at Cardiff University: Andrea, Alexandre, Antoine , Nicolas, Andrea, Rodolfo, Lou, Cataldo, Dmytro, Olesia, Elisa, Andrey, and Matte o, Tommas o, and Oliwia . I am also thankful to all the other lab mates and friends I’ve met at the Université de Namur (Belgium) and Università di T rieste (Italy). II Table of contents Table of Contents ABSTRACT ................................ ................................ ................................ ................................ V LIST OF ABBREVIATIONS ................................ ................................ ................................ ......... VII CHAPTER 1: INTRODUCT ION ................................ ................................ ............................... 1 1.1 BORAZINE -DOPED CARBON STRUCTU RES : SYNTHESIS AND APPLIC ATIONS ......................... 1 1.1.1 Synthesis of the borazine core ................................ ................................ ....................... 3 1.1.1.1 (1+1 ’+1+1 ’+1+1 ’) hexamerization via dehydrogenation reactions ................................ ...................... 4 1.1.1.2 (1+1 ’+1+1 ’+1+1 ’) hexamerization via condensation reactions ................................ ............................ 6 1.1.1.3 (2+2+2 ) trimerization and ‘inner shell ’ fusion ................................ ................................ ...................... 7 1.1.2 Reactivity of the B 3N3 core ................................ ................................ ............................ 9 1.1.2.1 Chemical stability and reactivity of the B 3N3 core ................................ ................................ ............... 9 1.1.2.2 Electrophilic additions at the B 3N3 core ................................ ................................ .............................. 10 1.1.2.3 Exchange reactions at the boron site ................................ ................................ ................................ ... 11 1.1.3 Functionalization of the inner shell ................................ ................................ ............ 13 1.1.4 Compatibility of borazine derivatives towards reagents and conditions .................... 15 1.1.5 Applications ................................ ................................ ................................ ................ 17 1.1.5.1 On -surface self -assembled architectures ................................ ................................ ............................. 18 1.1.5.2 Materials for storage of H 2 ................................ ................................ ................................ .................. 22 1.1.5.3 Materials for optoelectronic devices ................................ ................................ ................................ ... 23 1.1.5.4 Towards BN -doped carbon nanostructures ................................ ................................ ......................... 24 1.1.6 General considerations on borazine and its derivatives ................................ ............. 27 1.2 BRANCHED POLYPHENYLEN ES ................................ ................................ ........................... 28 1.2 .1 Overview and synthesis ................................ ................................ ............................... 28 1.2.2 Applications and bottom -up construction of functional systems ................................ 33 1.2.2.1 Weakly coordinating ions ................................ ................................ ................................ .................... 33 1.2.2.2 Bulky ligands for transition metals ................................ ................................ ................................ ..... 34 1.2.2.3 Photophysical study of branched polyphenyle nes ................................ ................................ .............. 36 1.2.2.4 Phenylene -based energy harvesting systems ................................ ................................ ....................... 40 1.2.2.5 P recursors for graphene substructures ................................ ................................ ................................ 47 1.2.3 General considerations on branched polyphenylenes ................................ ................ 49 CHAPTER 2: AIM OF TH E WORK ................................ ................................ ...................... 50 2.1 BOTTOM -UP SYNTHESIS OF BN -DOPED POLYPHENYLENES HAVING DIFFERENT DOPING DOSAGE AND ORIENTATI ON ................................ ................................ ................................ ..... 50 2.2 SYNTHESIS OF A BN -POLYPHENYLENE ENERGY HARVESTING SYSTEM ............................ 57 2.3 SYNTHESIS OF BORAZINE -DOPED GRAPHENE SUBST RUCTURES ................................ ......... 58 CHAPTER 3: RESULTS A ND DISCUSSION ................................ ................................ ....... 61 III Table of contents 3.1 BOTTOM -UP SYNTHESIS AND CHA RACTERIZATION OF BOR AZINE -DOPED POLYPHENYLENES ................................ ................................ ................................ .................... 61 3.1.1 Synthesis of borazine -doped building blocks ................................ .............................. 61 3.1.2 Synthesis of full -carbon building blocks ................................ ................................ ..... 68 3.1.3 Bottom -up synthesis of borazine -doped pol yphenylenes ................................ ............ 71 3.1.3.1 Synthesis of BN -polyphenylene with r= 2.8% ................................ ................................ ................... 71 3.1.3.2 Synthesis of BN -polyphenylene with r= 8.3% ................................ ................................ ................... 73 3.1.3.3 Synthesis of BN -polyphenylene with r= 7.1% ................................ ................................ ................... 78 3.1.3.4 Synthesis of BN -polyphenylene with r= 1.1% ................................ ................................ ................... 80 3.1.3.5 Synthesis of full -carbon polyphenylene and reference molecules ................................ ...................... 80 3.1.4 Spectroscopic studies of hybrid BNC polyphenylenes ................................ ................ 82 3.1.4.1 Monomeric and reference derivatives ................................ ................................ ................................ 85 3.1.4.2 Hexa -branched polyphenylenes ................................ ................................ ................................ .......... 86 3.1.4.3 Three -branched borazine -doped polyphenylenes ................................ ................................ ................ 88 3.2 SYNTHESIS OF A MULTICHROMOPHORIC BNC HYBRID POLYPHENYLENE ......................... 90 3.2.1 Synthesis of blue -labelled borazine -doped polyphenylene ................................ ......... 90 3.2.2 Photophysical characterization and estimation of the energy transfer ...................... 93 3.3 SYNTHESIS OF BORAZINE -DOPED PAH S AND GR APHENE -LIKE STRUCTURES .................... 98 3.3.1 Synthesis of borazine -polyphenylene precursors ................................ ........................ 98 3.3.2 Synthesis of a borazine -doped PAH with extended conjugated area ....................... 108 3.3.3 Perspectives towa rds the planarization of borazine -doped polyphenylenes ............ 111 3.4 CONCLUSIONS ................................ ................................ ................................ .................. 118 CHAPTER 4: EXPERIMEN TAL SECTION ................................ ................................ ....... 121 4.1 GENERAL REMARKS ................................ ................................ ................................ ......... 121 4.2 EXPERIMENTAL DETAILS FOR SECTION 3.1 ................................ ................................ ...... 123 4.3 EXPERIMENTAL DETAILS FOR SECTION 3.2 ................................ ................................ ...... 158 4.4 EXPERIMENTAL DETAILS FOR SECTION 3.3 ................................ ................................ ...... 16 3 4.5 CRYSTALLOGRAPHIC DATA ................................ ................................ .............................. 172 4.6 APPENDIX ................................ ................................ ................................ ......................... 179 CHAPTER 5: BIBLIOGRA PHY ................................ ................................ ........................... 225 IV Abstract Abstract Figure 1. Representation of general polyphenylene structures differentiating in