Acetylenic scaffolding with subphthalocyanines – synthetic scope and elucidation of electronic interactions in dimeric structures

Abstract

Boron subphthalocyanines (SubPcs) are powerful chromophoric heterocycles that can be synthetically modified at both axial and peripheral positions. Acetylenic scaffolding offers the possibility of building large, unsaturated carbon-rich frameworks that can exhibit excellent electron-accepting properties, and when combined with SubPcs it presents a convenient method for preparing interesting chromophore-acceptor architectures. Here we present synthetic methodologies for the post-functionalization of the relatively sensitive SubPc chromophore via acetylenic coupling reactions. By gentle AlCl-mediated alkynylation at the axial boron position, we managed to anchor two SubPcs to the geminal positions of a tetraethynylethene (TEE) acceptor. Convenient conditions that allow for stepwise desilylations of trimethylsilyl (TMS) and triisopropylsilyl (TIPS) protected SubPc-decorated acetylenes using silver(i) fluoride were developed. The resulting terminal alkynes were successfully used as coupling partners in metal-catalyzed couplings, providing access to larger acetylenic SubPc scaffolds and multiple chromophore systems. Moreover, conditions allowing for the conversion of a terminal alkyne into an iodoalkyne in the presence of SubPc were developed, and the product was subjected to cross-coupling reactions affording unsymmetrical 1,3-butadiynes. The degree of interactions between two SubPc units as a function of the acetylenic bridge was studied by UV-Vis absorption spectroscopy and cyclic voltammetry. A TEE bridging unit was found to strongly influence the reductions and oxidations of the two SubPc units, while a more flexible bridge had no influence.

Donor−Acceptor‐Functionalized Subphthalocyanines for Dye‐Sensitized Solar Cells

“…One‐electron oxidations to reactive radical cations are observed for 1 and 2 at E o ’=0.57 and 0.59 V, respectively, and small peaks corresponding to the reduction of one or more cations formed during the follow‐up reactions of the radical cations are observed close to 0.0 V during the backward scan. This behavior is typical for SubPc derivatives ,. The presence of the N , N ‐dimethylaniline unit in 3 causes this compound to behave quite differently.…”

Exploring the Synthesis and Electronic Properties of Axially Substituted Boron Subphthalocyanines with Carbon‐Based Functional Groups

“…[24] The approach to synthesizing Ph-(C≡C) n -BsubPcs and IPh-(C≡C) n -BsubPcs involved an intermediate TMS-(C≡C) n -BsubPcs, since it is possible to deprotect the TMS acetylene situated on the axial position of the BsubPc. [21] The removal of the TMS group is afforded by the use of silver fluoride and acetic acid and has previously [21] been shown to be effective for peripherally hydrogenated BsubPcs, unlike the standard deprotection conditions with tetrabutylammonium fluoride or potassium hydroxide.…”

“…[20] This method has been used on BsubPcs with hydrogens in the periphery and has enabled the formation of complex structures, like BsubPc dimers connected via acetylenic scaffolds. [21,22] We Figure 1. (A) The chemical structure of a boron subphthalocyanine (BsubPc) depicting the axial and peripheral positions.…”

Oligoyne-bridged boron subphthalocyanine dimers – synthesis and redox properties

“…The quality of the data is somewhat poor (and there are disordered solvent molecules), but the data are at least good enough to confirm the structure. Structural confirmation of SubPcs often proves challenging when relying only on NMR spectroscopy due to missing carbon resonances 5,18,20 (as experienced also for the compounds included in this work). In 13 C NMR spectroscopic analysis, a dampening of signal intensity (as a result of broadening) for 13 C nuclei in vicinity of boron ( 1 J to 4 J) is observed, related to carbon-boron spin-spin coupling.…”

“…17 However, by bridging SubPc units by a tetraethynylethene bridge as in compound 2 some changes in redox properties were observed. 18 The two SubPc units were reduced in a reversible two-electron process at a potential of -1.57 V vs Fc/Fc + ; this potential is similar to that of the monomer, but the reduction peak was unusually sharp, which may indicate potential inversion where the monoanion is easier to reduce than the neutral precursor on account of an internal reorganization of the structure. Moreover, the oxidation of the two SubPc units was observed to occur sequentially at +0.54 V and +0.65 vs Fc/Fc + , which indicates a Coulomb interaction between the two units.…”