Highly twisted quasi-aza[8]circulene and planar triazaoxa[8]circulene have been prepared, which exhibited intriguing optical properties.

We report here the synthesis of two novel subporphyrins (SubPs), in which the macrocycle has been functionalized at its meso (1) or axial (2) position with tetracyanobuta-1,3-diene (TCBD)–aniline. In-depth spectroscopic, spectrometric, and electrochemical analyses were carried out with both of them, whose molecular structures were determined by single-crystal X-ray diffraction studies. In the case of 2, its R a and S a enantiomers were separable by chiral HPLC and presented a fairly good configurational stability at room temperature, which enabled determining the activation parameters for the thermally induced racemization. Conversely, the enantiomers’ separation was unfeasible for 1 due to the conformational and/or configurational dynamics of the TCBD–aniline, a structural “flexibility” that could be drastically reduced at low temperatures. The physicochemical impact of placing the TCBD–aniline at either the axial or peripheral positions of SubPs is also rather significant. The HOMO–LUMO gap is reduced by as much as 0.35 eV in SubP–(TCBD–aniline) meso 1 (1.77 eV) and, in turn, enables an emissive charge-transfer (CT) state in virtually all environments. It is only in polar environments, where it links a local excitation with an indirect charge separation. In contrast, a much larger HOMO–LUMO gap of 2.12 eV in SubP–(TCBD–aniline)axial 2 disables an emissive CT state and enforces either an exciplex deactivation in apolar environments or a direct charge separation in polar environments.

A pentabenzopentaaza [10]circulene has been synthesized as the largest fully conjugated hetero [n]circulene via a fold-in oxidative fusion reaction of an ortho-phenylenebridged cyclic pyrrole pentamer. This circulene takes a saddle-distorted structure with bond lengths of the central tenmembered-ring in the range of 1.455-1.493 Å. Relatively broad absorption and fluorescence spectra were observed, which reflects its flexible structure, in accordance with the low-temperature NMR spectra and theoretical calculations. The energy barrier for saddle-to-saddle interconversion was estimated to be quite small ( � 3 kcal mol À 1 ).

Hetero[8]circulenes have emerged as novel functionalized heteronanographenes that show various promising functions such as bright fluorescence, charge transporting, and redox reactivities. One of the effective synthetic strategy is the fold‐in type oxidative fusion reaction of ortho‐phenylene‐bridged cyclic tetrapyrroles, whose construction, however, is not well‐sophisticated in terms of reproducibility and possibility for versatile derivatization. In this paper, a “reverse” coupling strategy has been developed, which enabled synthesis of opp‐type low symmetric analogues of cyclic tetrapyrroles. Oxidative fusion reaction conditions to afford tetraaza[8]circulenes have also been reinvestigated and improved. Substituent effects of cyclic tetrapyrroles and tetrabenzotetraaza[8]circulenes are studied for solid‐state structures and packing structures, redox potentials, and optical properties.