1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

1 Introduction
1.1 Porphyrins – A General Survey
1.1.1 Structures & Nomenclature
The term “porphyrin” is derived from the Greek word πορψυρά meaning purple and stands
for a huge class of organic molecules with a tetrapyrrolic structure, like e.g. 1. 14 Therein four
pyrrole rings are connected by methine bridges under formation of an aromatic macrocycle.
The basic porphyrin structure was first postulated by KÜSTER in 1912 15 and later verified by
FISCHER & ZEILE 16 . The simplest representative of that class is porphin 2, which is displayed in
Scheme 2. There, it is also illustrated, how the different positions on that system can be
denominated.
4
1
δ
8
α
2 3
NH N
NH N
21 22
β 20
24 23
N HN 19 N HN
γ
7 6
4
5
2
1
18
3 4 5 6 7
17 16 15 14 13
Scheme 2. Structure of porphin 2 with numbering systems according to FISCHER 17 (left) and to
IUPAC (right) 18 .
The elder nomenclature system introduced by FISCHER 17 has been based on several trivial
names. Synthetic systems could be referred to using descriptors which have been introduced
for the β- (blue) and the meso-positions (green) since they, in contrast to the α-positions
(red), can carry substituents (Scheme 2). While the latter were left unspecified, the β-
positions were numbered clockwise from 1 to 8 and the meso-positions were given Greek
letters. With the ongoing development of artificial systems, the names given became
complicated and ambiguous. Hence, the IUPAC introduced a systematic and clear
nomenclature system 18 which has mostly replaced the FISCHER system, being only used for
natural or semi-natural derivatives today. This newer system, also applied in this work, is
numbering each position of the macrocycle. Side chains can be referred to as usual by
8
9
10
11
12
indicating substituted positions by exponents as it is depicted in Scheme 3.
2