Synthesis, Structures, and Optical and Electrochemical Properties of Benzoporphycenes

Abstract

The first facile syntheses of free-base di- and tetrabenzoporphycenes and their metal complexes are reported, based on retro-Diels-Alder reactions of the corresponding bicyclo[2.2.2]octadiene-fused porphycenes, prepared by McMurray coupling of alpha,alpha'-diformyldipyrrole. The photophysical and electrochemical properties are analyzed based on UV/Vis absorption, magnetic circular dichroism (MCD), and fluorescence emission, lifetime and quantum yield measurements, cyclic and differential pulse voltammetry (CV and DPV) and time-dependent DFT calculations based on B3LYP geometry optimizations. Benzoporphycenes are found to be prime candidates for future use in photodynamic therapy.

First Synthesis of Dodecasubstituted Porphycenes

“…The B band is observed at a similar wavelength a 1 c, www.chemeurj.org but the Q band was about 100 nm redshifted compared with 1 a and an oscillatory structure was not observed for 1 a. Porphycene 1 b also showed a similar spectrum to that of 1 a. Porphycene 3 b showed broad peaks, as shown in Figure 5 a, although 3 c [10] showed a similar spectrum to that of 1 c with a clear oscillatory structure. [10] The absorption spectra of benzoporphycenes are also shown in Figure 5 a. The B band was observed at 450 nm, and the Q band reached to about 820 nm as a very broad band for 2 a and 2 b.…”

“…The synthesis of porphycenes 1 c, 2 c, and 3 c has been reported already. [10] The 1 H NMR spectrum of porphycene 1 a is shown in Figure 4 with that of porphycene 1 c. The meso protons at d = 9.77 ppm of 1 c disappeared for 1 a and ethyl proton signals appeared at d = 4.4 and 1.8 ppm. The NH protons of 1 c appeared at 0.8 ppm.…”

“…Porphycenes 1 a and 1 b were quantitatively converted into tetraalkyltetrabenzoporphycenes 2 a and 2 b, respectively, at 220 8C in vacuo. 2,7,12,10,19, was also prepared as a reference compound from bipyrrole 9 [10] in two steps, but 2, 7,12,17-tetrahexyl-9,10,19,20-tetraethylporphycene (3 a) was not successfully prepared. The synthesis of porphycenes 1 c, 2 c, and 3 c has been reported already.…”

“…Bipyrrole 7 [10] was doubly acylated by a Vilsmeyer-type reaction to give 8 a and 8 b in 80 and 97 %, respectively. The obtained products 8 a and 8 b were used in a McMurry-type coupling to give dodecasubstituted porphycenes 1 a and 1 b in 7.7 and 8.5 % yield, respectively.…”

“…Tuning of the electronic properties of porphycenes has been only attempted by introducing b substituents, [7] meso substituents, [8] p expansion, [9,10] and core modification. [11] This is mainly owing to the difficulty of introducing more than two meso substituents into b-octasubstituted porphycenes.…”