Cyclo[8]isoindoles: Ring‐Expanded and Annelated Porphyrinoids

Abstract

Retro: Cyclo[8]isoindole, which has a saddle‐shaped geometry (see picture, 2), was synthesized by oxidative coupling of a bicyclo[2.2.2]octadiene(BCOD)‐fused 2,2′‐bipyrrole followed by a retro‐Diels–Alder reaction of BCOD‐fused cyclo[8]pyrrole (1). Key trends in the optical spectra of ring‐annelated cyclo[8]pyrroles are identified based on magnetic circular dichroism spectra and theorectical calculations.

Acenaphthylene‐Fused Cyclo[8]pyrroles with Intense Near‐IR‐Region Absorption Bands

“…Attempts were made to increase the yield by modifying the reaction conditions. CeA C H T U N G T R E N N U N G (SO 4 ) 2 was used as an oxidant with H 2 SO 4 , Na 2 SO 4 , and TBAHSO 4 (TBA = NA C H T U N G T R E N N U N G (nBu) 4 ) in a manner similar to the approach described in our previous report on cyclo [8]isoindole [3] to afford 1 a and 1 b (R f = 0.6 and 0.9, respectively) in 33 and 7 % yields, respectively ( Table 1, entry 2). Cyclo [8]pyrroles 1 a and 1 b were obtained in moderate yields in the absence of Na 2 SO 4 and H 2 SO 4 ( Table 1, entries 3 and 4).…”

“…Recently, we reported the first example of a p-expanded cyclo [8]pyrrole, namely cyclo [8]isoindole (Figure 1), which has a slightly red-shifted absorption band at l = 1078 nm. [3] Sessler and Panda subsequently reported a cyclo [4]naphthobipyrrole compound that has a red-shifted near-IR absorption band which lies beyond l = 1200 nm. [4] Fused ring expansion of the pyrrole moieties at the b positions results in nonplanarity due to the steric effects between adjacent fused-benzene moieties.…”

Synthesis, Characterization, and Electronic Structures of Porphyrins Fused with Polycyclic Aromatic Ring Systems

“…The introduction of different fused ring moieties at the b-carbon atomso ft he pyrrole rings is used to fine-tunet he optical properties. As reportedp reviously for acenaphthylene-fused porphyrins, [21] an excitation wavelength dependencei so bserved in the emission spectra of some of the compounds. The trendso bserved in the opticalp roperties can be readily rationalized by using the Michl perimeter model to analyze the results of TD-DFT calculations.…”

“…Small changes are observed in the relative intensity of the emission peaks of 6f and 6g upon excitation at wavelengths similar to those reported for free-base acenaphthoporphyrins. [12,21] No such dependence was observed in the emission spectra of p-expanded porphyrins 3f and 3g,h owever, which have acenaphthalene moieties fused along the y axis in addition to the benzofluoranthene rings ystem (Figure 2a nd Figure S3 in the SupportingI nformation). These resultsindicate that each tautomer of 3f and 3g either has similara bsorption and emission properties or the formation of one of the tautomers is energeticallyf avored due to the presence of the fused aromatic ring systems.…”

“…Recently,w ereported that the absorption and emissionp roperties of acenaphthylene-fused porphyrins exhibit excitation-wavelength-dependent properties due to the presence of two NH tautomers in solution. [12,21] The excitation wavelength dependence of the fluorescencew as also examined for 3d-g, 6f,a nd 6g.A marked wavelength dependence is observed in the F values for 6g,b ut not for 3g ( Figure S3 in the Supporting Information). Small changes are observed in the relative intensity of the emission peaks of 6f and 6g upon excitation at wavelengths similar to those reported for free-base acenaphthoporphyrins.…”