Delving into Group 16 – Increasing the Accessibility and Understanding the Optoelectronic Properties of Tellurophenes

Abstract

This Thesis describes the investigation of 5-membered heterocycles that contain the heavy atom tellurium (Te), termed tellurophenes, as light emitting materials or the active (light absorbing) component in organic photovoltaics. A particular focus was placed on developing new routes to synthesize tellurophenes as well as studying their room-temperature phosphorescence (RTP). To begin, the emission of borylated tellurophenes was explored by revisiting the emission of a previously reported bis(pinacolatoboryl)tellurophene. This work concluded that the boron centres in this borylated tellurophene are largely involved in the photophysical process of RTP and found that the Lewis acidity of the boron centres could be used to tune the emission via coordination chemistry. Next, a new tellurophene precursor featuring di(isopropoxy)boryl –B(OiPr)2 groups was developed. This –B(OiPr)2 substituted tellurophene precursor underwent exchange reactions with alcohols and amines, including catechol, 4-tert-butylcatechol, and 1,8-diaminonaphthalene, to replace the OiPr groups on the boron centres with either oxygen- or nitrogen-based chelates. This method was used to synthesize three new borylated tellurophenes, which were all emissive when cooled to 77 K. Furthermore, the –B(OiPr)2 substituted tellurophene precursor could be reacted with MesMgBr (Mes = 2,4,6-Me3C6H2) to displace one OiPr group on each boron centre, yielding a new tellurophene (Mes(iPrO)B-Te-6-B(OiPr)Mes) that exhibited bright yellow RTP in the solid state. In addition to their emissive properties, borylated tellurophenes are also desirable precursors for Suzuki-Miyaura cross-coupling, leading to the formation of π-conjugated materials. However, tellurophenes often undergo facile protodeboronation under the basic conditions of these reactions, greatly reducing product yields. Therefore, the conditions for this reaction were optimized for tellurophenes, and the Suzuki-Miyaura cross-coupling of borylated tellurophenes with arylhalides under mild conditions with high isolated yields was reported. This synthetic route was then used to synthesize several 2,5-bis(aryl)tellurophenes, many of which exhibit RTP when incorporated into a rigid poly(methylmethacrylate) (PMMA) matrix. Finally, a new class of π-extended tellurophenes featuring a fused benzobithiophene core, termed tellura(benzo)bithiophenes (Te-bbts), were developed. One such Te-bbt with cumenyl (4-isopropylphenyl) side groups exhibited orange coloured phosphorescence in a rigid PMMA environment with an emission maximum (em) centred at 680 nm. A dibrominated Te-bbt monomer was also synthesized and later polymerized to give a novel Te-containing homopolymer with a broad absorption profile that extends beyond 600 nm. The results described in this Thesis demonstrate that tellurophenes are an attractive class of heterocycle with many useful properties, making them worthwhile targets for future research explorations.