Tellura(benzo)bithiophenes: Synthesis, Oligomerization, and Phosphorescence.

A series of planar π-extended Te-containing heteroacenes, termed tellura(benzo)bithiophenes, were synthesized. This new structural class of heterocycle features a tellurophene ring fused to a benzobithiophene unit with aromatic side groups (either -C6H4iPr or -C6H4OCH3) positioned at the 2- and 5-positions of the tellurophene moiety. Although attempts to enhance molecular rigidity and extend ring-framework π-delocalization in a cumenyl (-C6H4iPr)-capped tellura(benzo)bithiophene led to oxidation (and Te-C bond scission) to form a diene-one, the formation of an oligomeric tellura(benzo)bithiophene was possible via Kumada catalyst-transfer polycondensation (KCTP). Furthermore, one tellura(benzo)bithiophene derivative exhibits orange-red phosphorescence at room temperature in air when incorporated into a poly(methyl methacrylate) host; accompanying TD-DFT computations provided insight into a potential mechanism for the observed phosphorescence.

Using boryl-substitution and improved Suzuki-Miyaura cross-coupling to access new phosphorescent tellurophenes.

A new di(isopropoxy)boryl -B(OiPr)2 tellurophene precursor is described, from which several previously inaccessible phosphorescent borylated tellurophenes are formed via exchange of the -OiPr groups. One such tellurophene Mes(iPrO)B-Te-6-B(OiPr)Mes, bearing a sterically encumbered mesityl (Mes) substituent at each boron center, exhibits bright yellow-orange phosphorescence in the solid state at room temperature and in the presence of the known quencher O2. Furthermore, Suzuki-Miyaura cross-coupling between the newly prepared borylated tellurophenes and the test substrate 2-bromothiophene was examined with the pre-catalyst Cl(XPhos)Pd(aminobiphenyl). While more electron deficient boryl groups such as catecholatoboryl (-Bcat) yield significant protodeboronation in place of productive C-C bond formation, efficient formation of the desired thiophene-capped tellurophene thienyl-Te-6-thienyl was noted from tellurophenes bearing the readily accessible pinacolatoboryl (-Bpin) and 1,8-naphthalenediaminatoboryl (-Bdan) functional groups. These findings open the door for the efficient synthesis of aryl tellurophenes and polytellurophenes via the ubiquitous Suzuki-Miyaura coupling of borylated tellurophenes, which was previously hampered by protodeboronation.

Self-Assembly of Macrocyclic Boronic Esters Bearing Tellurophene Moieties and Their Guest-Responsive Phosphorescence.

Guest-controlled diastereoselective self-assembly of a diboryltellurophene and a chiral tetrol bearing an indacene backbone was achieved to give either hetero- or homochiral macrocyclic boronic esters, selectively. The heterochiral isomer (hetero-[2+2]Te ) exhibited a higher inclusion ability for electron-deficient aromatic guests, leading to effective quenching of phosphorescence from the diboryltellurophene moieties. The reported macrocycles collectively represent a promising arene sensing approach based on phosphorescence.

Moving Beyond Boron-Based Substituents To Achieve Phosphorescence in Tellurophenes.

Previous research in our group showed that tellurophenes with pinacolboronate (BPin) units at the 2- and/or 5-positions displayed efficient phosphorescence in the solid state, both in the presence of oxygen and water. In this current study, we show that luminescence from a tellurophene is possible when various aryl-based substituents are present, thus greatly expanding the family of known (and potentially accessible) Te-based phosphors. Moreover, for the green phosphorescent perborylated tellurium heterocycle, 2,3,4,5-TeC4BPin4 (4BTe), oxygen-mediated quenching of phosphorescence is an important contributor to the lack of emission in solution (when exposed to air); thus, this system displays aggregation-enhanced emission (AEE). These discoveries should facilitate the future design of color tunable tellurium-based luminogens.

Probing the nature of peripheral boryl groups within luminescent tellurophenes.

In this article our attempts to tune the color of luminescence within a new class of aggregation-induced emission (AIE) active tellurophenes is reported along with computational details that include spin-orbit coupling effects so as to better understand the nature of emission in the phosphorescent tellurophene (B-Te-6-B). Despite not meeting some of the initial synthetic targets, the emission within a borylated tellurophene can be altered with the addition of an N-heterocyclic carbene.