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Co-sensitization is an attractive approach to enhance the light-harvesting efficiency of a dye sensitized solar cell (DSSC), whereby two or more dyes having complementary absorption spectra are co-adsorbed within a DSSC. A new method of co-sensitizing simultaneously pyridyl- and carboxylic acid-based dyes was performed and proved to be a successful approach for increasing the photoconversion efficiency (PCE%) of a DSSC. Yellow and red pyridyl-based dyes (T181 and T202) were co-sensitized with a blue carboxylic acid-based dye (Dyenamo Blue, DB). The co-sensitized DSSCs showed profound performance enhancements with a cobalt tris­(bipyridine) electrolyte system. Increases in the total cell efficiency of 45% and 16% were seen in the co-sensitized T181-DB and T202-DB cells when compared to the single dye-sensitized DB cell, respectively. Remarkable increases in photocurrent (J sc) and photovoltage (V oc) were seen in both co-sensitized cells. The higher V oc values were mainly due to the decrease in the electron recombination processes at the TiO2/cobalt electrolyte interface. The increase in dye coverage in the co-sensitized cells resulted in a blocking behavior at the TiO2/electrolyte interface and had positive effects on electron lifetime. In addition the higher J sc values were associated with the complementary absorption responses of T181 and T202 with DB as mirrored in the IPCE% spectra.

Embedding seven-membered rings into polycyclic aromatic molecules is attractive as they can exert an influence on molecular conformation that ultimately changes the solubility and π-electronics. The considerations in designing and synthesizing a highly strained azatriseptane framework is discussed herein. We employ a twofold macrocyclization strategy to form the [7,7,7]-system and through scoping various strategies identify a Friedel-Crafts approach is key. The synthetic limitations we have identified, in addition to the successes presented here, highlights the key challenges in forming triseptane frameworks and paves the way for secondgeneration analogues that may have various applications in optical as well as electronic organic materials.

The synthesis and characterization of heptagonembedded polycyclic aromatic compounds are essential for understanding the effect of negative curvature on carbon allotropes such as fullerenes and graphenes that have applications in functional organic materials. However, owing to the synthetic difficulties in functionalizing and embedding seven-membered rings, these strain-challenged structures are relatively unexplored. We report here the synthesis, characterization, and properties of a triarylamine core bridged with ethano chains at the 2,2'-positions. In doing so, we provide access to the first heterocycle containing three fused heptagon rings with a nitrogen at its core (BATA-NHAc). X-ray crystallographic analysis and DFT calculations revealed a remarkably strained structure wherein two of the bridged aryl units approach coplanarity, while the third ring is twisted out of plane at 70°. UV-vis and emission spectroscopies identify red-shifted absorption and concentration-dependent emission profiles, respectively, as a result of the unique conformation and self-assembly properties of BATA-NHAc. Furthermore, cyclic voltammetry shows a decrease in the oxidation potential for BATA-NHAc in comparison to the non-bridged analog. This study opens new avenues in understanding the structure-property relationships of curved π-aromatics and the construction of π-frameworks of increasing complexity.

Invited for the cover of this issue is the group of Michel Rickhaus at the University of Zurich. The image depicts the “unearthing” of the highly contorted azatriseptane, a carbon framework consisting of three fused seven‐membered rings surrounding a central nitrogen. Read the full text of the article at 10.1002/chem.202203954.