Porphyrins with Exocyclic Rings. 16.¹ Synthesis and Spectroscopic Characterization of Fluoranthoporphyrins, a New Class of Highly Conjugated Porphyrin Chromophores

Abstract

Porphyrins with fused aromatic rings are under detailed investigation due to their unique spectroscopic properties. To gain more insights into the effects due to ring annealation on the porphyrin chromophore, a series of fluoranthoporphyrins have been synthesized. Reaction of 3-nitrofluoranthene with isocyanoacetate esters in the presence of a phosphazene base afforded good yields of the fluorantho[2,3-c]pyrrole esters 8. Cleavage of the ester moiety with KOH in ethylene glycol afforded the parent heterocycle 9, and this condensed with 2 equiv of acetoxymethylpyrroles 10 in refluxing acetic acid-2-propanol to afford tripyrranes 11. Following cleavage of the tert-butyl ester protective groups with TFA, "3 + 1" condensation with pyrrole dialdehyde 12 gave the fluoranthoporphyrins 13 in good overall yields. In addition, reaction of tripyrrane 11 with acenaphthopyrrole dialdehyde 16 gave the mixed acenaphthofluoranthoporphyrin 17 in excellent yields. A difluoranthoporphyrin 18 was also prepared via a "2 + 2" MacDonald condensation. Reaction of fluoranthopyrrole 8a with dimethoxymethane in the presence of p-toluenesulfonic acid gave the symmetrical dipyrrylmethane 19, and following ester saponification, this was condensed with a dipyrrylmethane dialdehyde to afford the adj-difluoranthoporphyrin 18. The UV--vis spectra for these fluoranthoporphyrins gave a series of three broadened absorptions in the Soret band region, although the Q-bands were little effected by ring fusion. The nickel(II), copper(II), and zinc chelates were more unusual, showing strong absorptions near 600 nm. Difluoranthoporphyrin 18 showed many of the same spectroscopic features, although the presence of two ring fusions gave rise to an increase in the spectroscopic shifts. The mixed system 17 gave spectra that showed larger red shifts due to the acenaphthylene unit combined with the features due to the fluoranthene rings. This work further demonstrates the utility of aromatic ring fusion in altering the properties of porphyrinoid systems.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

“…Pyrrole-fused fluoranthene 172.3 , later used as a precursor to peripherally fused porphyrins (Chart , section ), was synthesized by Lash et al in a modified Zard–Barton reaction (Scheme ). The inadequate reactivity of the starting 3-nitrofluoranthene 172.1 toward isocyanoacetates was overcome by using the strong phosphazene base 172.2 and reflux conditions.…”

Tuning the photophysical properties of BODIPY dyes through extended aromatic pyrroles

“…To further extend this procedure to more highly conjugated pyrroles, the readily available uorantho[2,3-c]pyrrole was chosen. 28 To obtain the dipyrrins based on this pyrrole; however, required heating at 140 C, considerably higher than the napthapyrrole based dipyrrins. Aer purication, the dipyrrins were converted to the BODIPY dyes 8 and 9 as previously described, Scheme 2.…”

Synthesis of isoindoles and related iso-condensed heteroaromatic pyrroles

“…The stability of this type of isoindole derives from their limited isoindole character and these compounds are best regarded as benzo-fused pyrroles. After further synthetic steps, these isoindoles have been applied in the form of di-, tri-, or tetramers as ruthenium containing photosensitizers, 32 and as 9,10-phenantroline-, 33 quinoline-, isoquinoline-, 34 fluoranthene-, 35 phenantro-, 36 naphto-, 37 pyreno- 38 and corannuleno-39 fused porphyrin analogues.…”