PORPHYRINS WITH EXOCYCLIC RINGS - 13 - SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF HIGHLY MODIFIED PORPHYRIN CHROMOPHORES WITH FUSED ACENAPHTHYLENE AND BENZOTHIADIAZOLE RINGS

As part of a survey on the influence of fused aromatic rings on the po rphyrin chromophore, a series of novel structures with fused acenaphth ylene or benzothiadiazole rings have been synthesized. Base-catalyzed condensation of 1-nitroacenaphthylene or 4-nitrobenzothiadiazole with esters of isocyanoacetic acid afforded good yields of the annelated py rroles 5 and 28. Cleavage of the ester moieties with KOH in refluxing ethylene glycol gave the unsubstituted heterocycles, and subsequent co ndensation with 2 equiv of acetoxymethylpyrroles 9 in acetic acid/etha nol produced the modified tripyrranes 12 and 31. Tripyrranes with term inal tert-butyl ester units were treated with TFA and condensed with 3 ,4-diethyl-2,5-pyrroledicarboxaldehyde 13 in dichloromethane to give, following oxidation with DDQ, the corresponding pi-extended porphyrins 14 and 32. Acenaphthoporphyrins 14 showed unique UV-vis spectra with a triply split Soret band region and a relatively strong band near 660 nm. Strongly red-shifted absorptions were also noted for the dication s and the nickel(II), copper(II), and zinc chelates for this system. T hiadiazoloporphyrins 32 gave two broadened Soret bands, but the Q-band region was unexceptional. However, the nickel(II), copper(II), and zi nc complexes all showed abnormally strong absorptions between 600 and 612 nm. Porphyrins with two antipodal fused aromatic rings were easily prepared by condensing c-annelated pyrroledialdehydes 17 with tripyrr anes 12 and 31, and the spectroscopic properties of the resulting porp hyrins showed that the observed ring-fusion effects were essentially a dditive. Porphyrins with two adjacent acenaphthylene rings were also p repared by the MacDonald ''2 + 2'' condensation, although this chemist rry gave poor results in the synthesis of a porphyrin with two fused b enzothiadiazole rings. The spectroscopic properties of these new highl y conjugated porphyrin structures show that ring fusion can profoundly modify the porphyrin chromophore.