Giant Conjugated Macrocycles: Synthesis and Applications

Abstract

Conjugated giant macrocyclic oligothiophenes 2Tn (n 2 4), 5Tn (n 2 6), and 6Tn (n 2 5) composed of 2,5 thienylenes, ethynylenes, and vinylenes with 24π to 180π electron systems have been synthesized using a modi ed McMurry coupling reaction as the key step. For the synthesis of cyclo[n](2,5 thienylene ethynylene)s nCTE (n 10 and 12) composed of 2,5 thienylenes and ethynylenes, a bromination dehydrobromination then double elimination procedure was employed. X ray analyses of 2T2 (24π), 5T2 (60π), and 6T2 (72π) revealed unique molecular and packing structures, re ecting their planar cyclic frameworks having medium to large inner cavities. Interestingly, giant macrocycles self aggregate in the solid state to form various nanostructures re ecting their nanophase separation, and the two photon absorption properties of 6Tn (n 2 5) show that increasing π conjugation leads to an increase in the two photon absorption cross section with magnitudes as high as 100,000 GM being realized. Furthermore, the giant macrocycle 6T5 behaves as a synthetic cyclic pigment comparable to the natural light harvesting system.

On-Surface Synthesis and Characterization of Honeycombene Oligophenylene Macrocycles

“…There are numerous examples for the synthesis of conjugated macrocycles in solution, , most of which use a combination of arylene and ethynylene building blocks to generate shape-persistent rings. − Macrocycles consisting exclusively of phenylene groups have rarely been made. , A drawback of the solution-based approach is that the large molecules and their precursors carry spacious substituents (typically alkyl chains with 6 to 12 carbon atoms), which are necessary to achieve sufficient solubility during synthesis, but are disadvantageous in other respects, because they can prevent efficient π-orbital overlap in molecular organic semiconductors, resulting in reduced charge carrier mobility, affect the two- or three-dimensional crystallization, and may have adverse effects in molecular machines . An illustrative example is the C 60 -wheeled “nanocar” molecule with its 12 C 10 H 21 chains .…”

New thiophene-based conjugated macrocycles for optoelectronic applications

“…These low values of E 1/2ox and shallow IE are typical of these types of thiophene-based macrocycles. 57,72,76 Surprisingly, a higher IE was observed for electrochemical measurements performed on McT-2 (À4.8 eV). Hence, based on these data, both McT-1 and McT-2 are considered donor type materials, with a fundamental gap (E fund ) of 2.1 eV and 1.6 eV, respectively (in accordance with the E opt obtained from solution), and can be used with PCBMs as acceptors in BHJ cells (see energy level diagram in Fig.…”

“…103,104 However, in this work the number of alkynes were minimised, contrasting with the most common thiophene-based macrocycles reported. 57,71,74 This leads to a challenging molecular arrangement of the parallel thiophenes since they usually tend to arrange in an anti-conformation when in a linear system. 92,101 In order to achieve an optimal yield by facilitating the cyclisation and suppressing polymerisation, the total concentration of the reacting species (compounds 1 and 2) was optimised as summarised in Tables S1 and S2 (provided in the ESI †).…”

“…52 Conjugated macrocycles appear in this scenario as an emerging family of materials with great potential for optoelectronic applications. [53][54][55][56] These materials possess unique features including their controlled structure that can facilitate intermolecular arrangement, 57 and their defined cavity that can be used to host electronically active molecules such as fullerene derivatives. 58,59 Furthermore, by virtue of their cyclic structure, they do not feature end-group functionalisation, which often result in charge traps in linear molecules.…”

“…Utilising the well-established McMurry reaction, alkynespaced building blocks were used in order to suppress steric hindrance and facilitate the cyclisation step, as is common when constructing such molecular systems. 57,74 However, considering results discussed in our previous report which pointed that alkyne spacers are detrimental to charge transfer, charge generation and ultimate photovoltaic performance in thiophene-based molecules, 102 the macrocycles were designed to minimise the number of alkyne groups compared to other reported systems, with only four present in each macrocycle. The synthesis of the new macrocycles was accomplished via dimerisation of two oligothiophene units, in which the concentration of the reacting species was key to yield the desired products.…”