Development of new efficient synthetic strategies leading to more
diversified substitution patterns of porphyrin rings is of great
importance as it expands the potential applicability of these
compounds and provides a more accurate way of tailoring their
properties for a specific application. Changes in the electronic and
conformational structures induced by different substituents are
manifested by unique properties which are of interest for many
applications ranging from amphiphilic porphyrins for
photodynamic therapy, push-pull systems for optical applications,
chiral systems useful in catalysis, to donor-acceptor systems
suitable for electron transfer studies. Different chemical strategies
were demonstrated for access to unsymetrically substituted
porphyrins with nonequivalent ?- or meso substituents. For the
latter we have adopted the functionalization of preformed
porphyrins
in order to obtain a diverse range of porphyrin structures with
5,15-A2B2 and 5,15-A2BC meso substitution patterns suitable
for applications in optical limiting and photodynamic therapy.
The functionalization of A2?type starting material via
organolithium and palladium catalyzed crosscoupling reactions
is an efficient means which enables the introduction of almost
any desired meso substituent. We report on the nonlinear
absorptive properties of our A2B2 and A2BC porphyrins and
show that there is strong correlation between structural features
and the optical limiting efficiency. The nonlinear optical studies
indicate that the 5,15-A2B2 substitution pattern provides more
promising candidates for use in optical limiting.
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Chemistry (Scholarly Publications)
Werner Blau,
Mathias Senge