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.
With peripheral fluorination and chlorination known to significantly influence the solubility, fluorescence quantum yield and redox properties of boron subphthalocyanines (BsubPcs), it is the intent of this study to further expand a matrix of BsubPcs to correlate structural changes to properties. Here, we have adapted previous synthetic methodologies for accessing axially substituted BsubPcs with a variety of alkyne substituents along with incorporating various peripheral halogens. While axial substitution of BsubPcs results in minimal shifts of longest-wavelength absorptions, relative fluorescence
Indenofluorene‐extended tetrathiafulvalenes (IF‐TTFs) comprise a class of π‐conjugated sensitizers that exhibit strong absorptions in the visible region and two reversible one‐electron oxidations. Herein we present the synthesis and optical as well as redox properties of novel IF‐TTF donor‐acceptor scaffolds that were integrated in dye‐sensitized solar cells (DSCs) via anchoring of a carboxylic acid end‐group on the scaffolds to TiO2. Synthetically, the scaffolds were constructed by Sonogashira coupling reactions between an iodo‐functionalized IF‐TTF and an acceptor moeity containing a terminal alkyne. These very first IF‐TTF based candidates for DSCs exhibited high performances, in particular a dye incorporating a benzothiadiazole acceptor moiety, showing a conversion efficiency of 6.4 %. This result signals that IF‐TTF derivatives present a promising class of compounds for further structural modifications. Such modifications will benefit from the readiness of the iodo‐funcitonalized IF‐TTF building block to undergo Pd‐catalyzed coupling reactions.
The promotion of mixed-valence interactions between redox-active, π-conjugated scaffolds is of interest when developing new conducting or electrochromic materials as well as in the construction of redox-controlled supramolecular assemblies. In this work, dimeric structures of the redox-active indenofluoreneextended tetrathiafulvalene (IF-TTF) unit were synthesized in a stepwise protocol. The synthesis relied on the development of a new unsymmetrical IF-TTF building block by a combination of phosphite-mediated and Horner−Wadsworth−Emmons reactions for introduction of the dithiafulvene units. The redox properties were studied by cyclic voltammetry, where it was observed that a first one-electron oxidation, corresponding to a mixed-valence state, occurs at a significantly lower potential when the IF-TTF unit is incorporated into a dimer, compared to a monomer analogue. This result indicates that locking the redox-active IF-TTF units in close proximity promotes intramolecular mixed-valence interactions. A computational study was also conducted, supporting the involvement of intramolecular interactions. Article pubs.acs.org/joc
A soluble, green‐blue fluorescent, π‐extended azatrioxa[8]circulene was synthesized by oxidative condensation of a 3,6‐dihydroxycarbazole and 1,4‐anthraquinone by using benzofuran scaffolding. This is the first circulene to incorporate anthracene within its carbon framework. Solvent‐dependent fluorescence and bright green electroluminescence accompanied by excimer emission are the key optical properties of this material. The presence of sliding π‐stacked columns in the single crystal of dianthracenylazatrioxa[8]circulene is found to cause a very high electron‐hopping rate, thus making this material a promising n‐type organic semiconductor with an electron mobility predicted to be around 2.26 cm2 V−1 s−1. The best organic light‐emitting diode (OLED) device based on the dianthracenylazatrioxa[8]circulene fluorescent emitter has a brightness of around 16 000 Cd m−2 and an external quantum efficiency of 3.3 %. Quantum dot‐based OLEDs were fabricated by using dianthracenylazatrioxa[8]circulene as a host matrix material.
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