2,5-Thienylene-Strapped Bicyclic and Tricyclic Expanded Porphyrins.

An [18]thiaporphyrin[36]dithiaoctaphyrin-[18]thiaporphyrin tricyclic macrocycle, fused through the 2,5-thienylene bridging moiety, was isolated during the preparation of 2,5-thienylene-strapped [26]hexaphyrin containing o-dichlorophenyl groups as meso substituents. The spectroscopic data of the 2,5-thienylene-strapped [26]hexaphyrin verified contributions of aromaticity from ring currents of both the [18]thiaporphyrin and the [26]hexaphyrin. The crystal structure of the tricyclic macrocycle revealed a distorted [36]dithiaoctaphyrin central core with two [18]thiaporphyrin sidewheels oriented nearly perpendicular to the mean-plane of dithiaoctaphyrin, implying the existence of independent π-conjugated systems. Both the absorption maximum at 441 nm and the chemical shifts in the 1 H NMR spectrum of the tricyclic macrocycle are dominated by diatropic ring currents of two aromatic [18]thiaporphyrin sidewheels.