Thiophene-Fused Nickel Dithiolenes: A Synthetic Scaffold for Highly Delocalized π-Electron Systems

Abstract

A series of thiophene-fused nickel dithiolene complexes have been prepared via synthetic methods which allow the addition of peripheral aryl groups to the fused thiophene of the dithiolene ligand, thus providing access to a range of structural and electronic modifications to the dithiolene core. X-ray structural studies of the anionic complexes show that the peripheral aryl rings lie in near-perfect coplanarity to the dithiolene core and can form π-stacked columns with N-methylpyridinium cations. Density functional theory calculations show significant delocalization of the frontier orbital electron density into the peripheral aryl rings. The complexes exhibit tunable, intense near-IR (NIR) absorption in the range of 1076-1160 nm with molar absorptivity as high as 25100 M cm in solution. The electronic tunability as well as the desirable solid-state packing arrangements of these systems suggests significant potential as NIR-absorbing materials for optoelectronic applications.

Thiophene‐Extended Nickel Thiazoledithiolene: π‐Extended Fused‐Ring Metal Dithiolenes with Stabilized Frontier Orbitals

“…This resulted in the growth of two different crystal types – large, black block‐like crystals, and a small proportion of red, needle‐like crystals. X‐ray diffraction of the black block‐like crystals gave the expected crystal structure of 8 (Figure ), which agrees well with the previously reported structure of 4 , . The two thiazoledithiolene ligands adopt the commonly observed trans configuration, and Ni–S bond lengths are observed ranging from 2.160 to 2.176 Å (Table ).…”

“…As shown in Scheme , the π‐extended nickel thizaoledithiolene 8 was prepared in a similar manner to the previously reported nickel thiophenedithiolene 4 , , . The application of regioselective cross‐coupling methods developed for 2,3,5‐tribromothiophene to 2,4,5‐tribromothiazole ( 5 ) gave the intermediate 6 in reasonable yield, followed by conversion to the acetyl‐protected thiazoledithiolate ligand 7 .…”

“…The application of regioselective cross‐coupling methods developed for 2,3,5‐tribromothiophene to 2,4,5‐tribromothiazole ( 5 ) gave the intermediate 6 in reasonable yield, followed by conversion to the acetyl‐protected thiazoledithiolate ligand 7 . As previously discussed in detail, the specified sequential addition steps in the generation of the acetyl‐protected ligands are necessary to inhibit the halogen dance reaction, typical of lithiated thiophenes and their heterocyclic analogues. Although the conversion of 6 to 7 occurred in somewhat limited yield, this is in good agreement with the previously reported thiophene species, and illustrates that the electronic differences between thiophene and thiazole had little effect on the synthetic methods employed.…”

“…However, an alternate approach to tuning these complexes is through the fusion of aromatic rings to the dithiolene core. Common examples of fused‐ring metal dithiolenes have included the fusion of benzene ( 2 ) and thiophene ( 3 ),, , with ring fusion increasing molecule planarity and enhancing orbital overlap, thus maximizing electron delocalization into the organic ligands.…”

“…With the goal of producing new hybrid materials that combine the characteristics of metal dithiolenes and oligothiophenes, the Rasmussen group has previously developed a series of π‐extended nickel thiophenedithiolenes ( 4 , Figure ) that exhibited unprecedented electronic delocalization, with low‐energy NIR transitions in the range of 1076–1160 nm , . In addition, this new family of nickel thiophenedithiolenes retained the characteristics of typical metal dithiolenes including rich electrochemistry, close contacts in the solid state, and magnetic or semiconducting properties, thus providing significant promise for the application of this new family of dithiolenes to optoelectronic devices.…”