In this article, we report the preparation of unprecedented p-conjugated macrocycles (Fig. 1) by acetylenic scaffolding using modular tetraethynylethene (TEE, 3,4-diethynylhex-3-ene-1,5-diyne) building blocks. A novel photochemical access to (Z)-bisdeprotected TEEs (Scheme 1) enabled the synthesis of the anilino-substituted perethynylated octadehydro[12]-(5) and dodecadehydro [18]annulenes (6) (Scheme 2). Following the serendipitous discovery of perethynylated radiaannulenes (Scheme 3) that can be viewed as hybrids between perethynylated dehydroannulenes and expanded radialenes, two series of monocyclic (7 ± 9; Scheme 6) and bicyclic (10 and 11; Scheme 7) representatives were prepared. Substantial strain in the macrocyclic perimeter of radiaannulene 7 was revealed by X-ray crystal-structure analysis (Fig. 2). Nevertheless, mono-and bicyclic radiaannulenes are stable at room temperature in air for months. The opto-electronic properties of both dehydroannulenes and radiaannulenes are substantially enhanced by the introduction of the peripheral anilino donor groups that undergo strong intramolecular charge-transfer interactions with the electron-accepting all-C cores. As a result, the UV/VIS spectra feature intense, bathochromically shifted charge-transfer bands that disappear upon protonation of the anilino moieties and are fully recovered upon neutralization (Figs. 4 ± 9). A comparison between anilino-substituted perethynylated dehydroannulenes, expanded radialenes, and radiaannulenes revealed that the efficiency of the intramolecular charge-transfer interaction strongly depends on the structure of the electron-accepting all-C perimeter. Electrochemical investigations (Table) demonstrated that the radiaannulenes are particularly powerful electron acceptors. Thus, bicyclic radiaannulene 11, which possesses eight peripheral 3,5-di(tert-butyl)phenyl substituents, is reversibly reduced at À 0.83 V in THF (vs. Fc / Fc), making it a better electron acceptor than buckminsterfullerene C 60 under comparable conditions.

A range of lipo- and hydrophilic derivatives of the new class of octaalkynyl tetra-[6,7]-quinoxalinoporphyrazines (TQuiPors), analogues of the naphthalocyanines, were prepared in two steps starting from functionalised hexa-1,5-diyne-3,4-diones. Divalent zinc and magnesium ions were introduced into the macrocyclic core. Whereas the triisopropylsilyl-, 3,5-di-tert-butylphenyl- and 4-triisopropylsilyloxyphenyl-terminated acetylenic TQuiPors are lipophilic and hence soluble in standard organic solvents, a polyethylene glycol-substituted derivative was found to dissolve in DMSO as well as in ethanol/water mixtures. The new chromophores are characterised by intense UV/Vis/NIR absorptions, most notably by bands at 770 nm with extinction coefficients exceeding 500 000 M(-1) cm(-1). With a view to possible photodynamic therapy applications, the potency of the chromophores to sensitise the formation of singlet oxygen was examined, both qualitatively using a 1,3-diphenylisobenzofuran assay, and quantitatively by the determination of the singlet oxygen quantum yields. It was found that all TQuiPors produce singlet oxygen when irradiated in the presence of air. In particular, the octaalkynyl Zn-TQuiPor generates singlet oxygen with a quantum yield of 56 %, thereby rivalling, and, in conjunction with its absorption profile, even exceeding the standards set by established PDT agents. The photostabilities of the TQuiPors were assessed and generally found to be satisfactory, but dependent on the solvent and the wavelength of the incident light.

Starting from (Z)-bis(N,N-diisopropylanilino)-substituted tetraethynylethene (TEE), perethynylated octadehydro[12]- and dodecadehydro[18]annulenes were prepared by oxidative Hay coupling. The dodecadehydro[18]annulene with six peripheral N,N-diisopropylanilino substituents was characterized by X-ray crystallography. Elongation of the Z-bisdeprotected TEE by Cadiot-Chodkiewicz coupling with 1-bromo-2-(triisopropylsilyl)ethyne provided a Z-configured bis(butadiyne), which after alkyne deprotection afforded under Hay coupling conditions N,N-diisopropylanilino-substituted perethynylated hexadecadehydro[20]- and tetracosadehydro[30]annulenes. The diisopropylanilino substituents enhance the properties of these unprecedented all-carbon perimeters in several distinct ways. They ensure their solubility, increase their stability, and importantly, engage in strong intramolecular charge-transfer interactions with the electron-accepting all-carbon cores, resulting in intense, bathochromically shifted charge-transfer bands in the UV/Vis spectra. The charge-transfer character of these bands was confirmed by protonation-neutralization experiments. The redox properties of the new carbon-rich chromophores were investigated by cyclic voltammetry and rotating disk voltammetry, which indicated different redox behavior for aromatic (4n+2 pi electrons) and antiaromatic (4n pi electrons) dehydroannulenes.

A novel class of planar, highly conjugated all-carbon macrocycles, which we christened "radiaannulenes", have been prepared based on acetylenic scaffolding using tetraethynylethene (TEE) building blocks; these structures are powerful electron acceptors and, upon peripheral substitution with electron-donating N,N-dialkylanilino groups, display intense intramolecular charge-transfer.