Phthalocyanine analogues. Part 1. Synthesis, spectroscopy, and theoretical study of 8,18-dihydrodibenzo[b,l]-5,7,8,10,15,17,18,20-octa-azaporphyrin and MNDO calculations on its related Hückel heteroannulene - Fernández-Lázaro F; De Mendoza J; Mó O; Rodriguez-Morgade S; Torres T; Yáñez M; Elguero J (Royal Chemical Society Journal Perkin Transactions 2, 1989)