Tellurophenes

The first preparation of a tellurophene, tetraphenyltellurophene, was reported in 1961 by Braye et al.[2][3] by reacting 1,4-dilithiotetraphenylbutadiene with tellurium tetrachloride, with the former synthesized by reaction of diphenylacetylene and lithium metal.

In 2008, Zeni et al. reported on the copper-catalyzed cyclizations of chalcogenoenynes to obtain 3-substituted chalcogenophenes which could be further functionalized using boronic acids via palladium-catalyzed Suzuki coupling.

The significantly higher Ka was found to be in agreement with density functional theory calculations which showed that the minimum-energy geometry was one where the chloride anion was in between the tellurium atoms, with Te–Cl bond distances of 3.23 Å and Cl–Te–C angles of 170°.

It was postulated that the low quantum yields were due to the fact that there were no lower energy excited states with Te-X antibonding character, and that this would limit the efficiency of the reaction.

Therefore, it was thought that by changing the substituents on tellurophene such that the main transition upon photoexcitation would be HOMO to LUMO, this would significantly improve the reaction by removing efficiency losses through relaxations from states that did not possess Te-X antibonding character and did not promote Te-X bond dissociation.In 2015, Seferos et al. demonstrated that 2,5-diphenyltellurophene (PT) could participate in photoreductive elimination of fluorine, chlorine, and bromine via the two-electron Te(IV)/Te(II) photocycle, with quantum yields of up to 16.9%.

Upon addition of halogen, however, it was found that the HOMO-LUMO energy gap decreased, with the LUMO possessing significant Te-X antibonding character.

In 2013, Seferos et al. reported the first example of a water-soluble tellurophene by attaching octaethylene glycol monomethyl ether (OEG) substituents on the para-position of the phenyl groups on 2,5-diphenyltellurophene.

The telluroketone was also found to be generated upon irradiation of a solution of the tellurophene in water with blue LED light, showing that it could be oxidized by singlet oxygen.

By analyzing the reaction by 1H NMR spectroscopy, it was found that the yellow solid that had formed as the product had a downfield shift at 1123.3 ppm upon addition of mCPBA.

Upon irradiation of a solution containing both PT and 9,10-DPA with white light, a decrease in the absorbance at 355 nm was observed, which was indicative of 1O2 formation since 9,10-diphenylanthracene undergoes 1,4-addition with 1O2 to form the endoperoxide.

The phosphorescence was found to be aggregation-induced, as the tellurophene was non-emissive when dissolved in THF, but glowed bright green in the solid state and upon aggregation in THF/water solutions.

By replacing the pinacolboronate esters with thiophenes, there was no luminescence, indicating that both Te(II) and BPin played a cooperative role leading to emission.

In 2018, Okuma et al. reported the synthesis of various 2,5-diaryltellurophenes substituted with electron-donating and electron-withdrawing groups through sequential ditelluride exchange and intramolecular cyclization reactions.

[26] By having both electron-donating (e.g. OMe) and electron-withdrawing (e.g. CN) groups on the tellurophene simultaneously, this resulted in a sharp reduction of the HOMO-LUMO gap.

It was concluded that having both electron-donating and electron-withdrawing substituents stabilizes the LUMO, with the HOMO-LUMO transitions having significant charge-transfer character, which in turn explained the solvatochromic effect.

From this, it was found that moving the ethyl branches away from the heterocycle to the more remote 3- and 4- positions led to an improved polymerization rate and control, such that P3ATe with narrow polydispersities and high molecular weights were obtained.

Furthermore, it was found that upon moving the branching point away from the heterocycle led to a red-shift in the optical absorption, which was attributed to a decrease in the degree of twisting, resulting in an increase in the conjugation between the tellurophene backbone.

Heeney et al. reported the synthesis of the first tellurophene-vinylene copolymer through Stille coupling of 2,5-dibromo-3-dodecyltellurophene and (E)-1,2-bis(tributylstannyl)ethylene, resulting in P3TeV in 57% yield with an approximate Mn of 10 kDa and a polydispersity of 2.4.

By constructing organic field effect transistors (OFETs), it was found that the selenophene polymer had the highest charge mobility, and that the tellurium analogue did not lead to an increase in mobility despite the larger size of tellurium, and possibility of closer interchain Te-Te interactions, which was attributed to the low solubility of P3TeV which resulted in poor film formation.

In 2015, Stephan et al. reported a vinyl telluroether with a pendant borane which acted as an intramolecular frustrated Lewis pair (FLP).

Reacting this compound with phenylacetylene at room temperature resulted in a cis-1,2-addition across the alkyne bond, generating a zwitterionic, six-membered Te-B heterocycle, as observed using X-ray diffraction spectroscopy.

Although the telluroether did not undergo oxidation by halogens to produce the corresponding Te(IV) dihalide compounds, it was found to react with iodine to afford a five-membered Te-B-I heterocycle.

Later, Stephan et al. reported the synthesis of various Te-B heterocycles through reaction of 1-bora-4-tellurocyclohexa-2,5-diene and two equivalents of a terminal alkyne upon heating, with loss of a diarylalkyne.

However, due to the relatively weak strength of hydrogen bonds, HOFs rarely exhibit permanent porosity upon removal of solvent molecules.

[36] Nonetheless, the weak interactions in HOFs allow the formation of single crystals, which are more amenable to crystallographic studies compared to COFs.

[36] In 2016, Seferos et al. reported the synthesis of HOFs from chalcogen heterocycles capped with N-methyliminodiacetic acid (MIDA) boronates which contain both hydrogen bond donors and acceptors.

Capliertellurophene
improvedsynthesis
5.05Wk4
Taylor Tellurophene
Synthesis of 2,4-difunctionalized tellurophenes.
Ethynylene-linked bistellurophene anion receptor [ 10 ]
(a). LUMO+1, (b). LUMO, (c). HOMO, and (d). HOMO-1 of 2,5-diaryltellurophene calculated with the B3LYP functional [ 13 ] and 6-31G(d) basis set [ 14 ] using Avogadro [ 15 ] and GAMESS. [ 16 ] [ 17 ]
Photoreductive elimination of halogens using 2,5-diphenyltellurophene (PT) [ 19 ]
Treatment of tellurophene with hydrogen peroxide [ 20 ]
Synthesis of a water-soluble tellurophene [ 20 ]
(a). LUMO+2, (b). LUMO+1, (c). LUMO, (d). HOMO, (e). HOMO-1 of telluroxide (PT-O) calculated with the B3LYP functional [ 13 ] and 6-31G(d) basis set [ 14 ] using Avogadro [ 15 ] and GAMESS. [ 16 ] [ 17 ]
Two different pathways for the photooxidation of 2,5-diaryltellurophene using oxygen and mCPBA [ 21 ]
Phosphorescent pinacolboronate-substituted tellurophenes
A 2,5-diaryltellurophene with electron-donating and electron-withdrawing groups [ 26 ]
(a). LUMO and (b). HOMO of p-anisyl and p-cyanophenyl substituted 2,5-diaryltellurophene calculated with the B3LYP functional [ 13 ] and 6-31G(d) [ 14 ] basis set using Avogadro [ 15 ] and GAMESS. [ 16 ] [ 17 ]
Synthesis of P3TeV using Stille coupling [ 30 ]
Synthesis of telluroether with pendant borane [ 31 ]
Synthesis of tellurium-boron heterocycles [ 33 ]
Chalcogen heterocycles capped with MIDA boronates [ 35 ]