First Synthesis of meso ‐Chlorinated Tetrabenzoporphyrins

meso ‐Chlorinated bicyclo[2.2.2]octadiene‐fused porphyrins 2 (Cl n TBCODPs; n = 1–4) have been synthesized by chlorination of the free base TBCODP‐H 2 ( 1 ‐H 2 ) using N ‐chlorosuccinimide (NCS). The chlorinated derivatives were easily separated by column chromatography on silica gel to give 2 ‐H 2 in good yields. This method for the chlorination of porphyrin using NCS is mild, safe, and economic compared with the established procedure for the meso ‐chlorination of porphyrins. We also discovered the unexpected meso ‐chlorination of the porphyrin with dichlorodicyanobenzoquinone (DDQ) by single‐electron transfer. Cl n TBCODPs 2 were converted into tetrabenzoporphyrins (Cl n TBPs) 3 in 100 % yields by retro‐Diels–Alder reaction. The derived compounds were characterized by NMR spectroscopy, UV/Vis spectrophotometry, cyclic voltammetry (CV), X‐ray crystallography, and organic field‐effect transistor (OFET) characteristics. The introduction of chlorine at the meso positions of the TBPs drastically changed their electronic and structural properties. The maxima of protonated Cl 4 TBP‐H 2 ( 3d ‐H 2 ; λ max = 494, 649, and 707 nm) were redshifted by around 50–65 nm relative to those of protonated TBP‐H 2 ( λ max = 431, 605, and 660 nm). The two Q‐band maxima of the Cl 4 TBP dication are similar to those of a tetraacenaphthoporphyrin dication ( λ max = 525, 646, and 702 nm), which has one of the most redshifted Q‐bands.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)