Synthesis, Spectroscopy, and Electrochemistry of Tetra‐tert‐butylated Tetraazaporphyrins, Phthalocyanines, Naphthalocyanines, and Anthracocyanines, together with Molecular Orbital Calculations

Abstract

Tetraazaporphyrins (TAPs), phthalocyanines (Pcs), naphthalocyanines (Ncs), and anthracocyanines (Acs) with four tert-butyl groups attached at similar positions have been synthesized, and their electronic absorption, magnetic circular dichroism (MCD), IR, and voltammetric properties were studied and interpreted with the help of quantum-mechanical calculations. Through the preparation of a series of compounds with the same number of the same substituent, the effects of the increase in the size of the ring system were clearly derived. The main results may be summarized as follows. 1) The Q band shifts to longer wavelength and its intensity increases, but with decreasing degree of change with increasing molecular size. If the size of the effect of benzene directly fused to the TAP skeleton is set at unity, the effects of the second and third benzene units are roughly 0.8 and 0.5, respectively. 2) The splitting of the Q bands in metal-free compounds decreases with increasing molecular size, so that the Q bands of H2Nc and H2Ac appear as single bands. 3) The magnitude of the orbital angular momentum of the excited state of the ligand decreases with increasing molecular size. 4) Interestingly, the ring current, as judged from the positions of pyrrole proton signals in the 1H NMR spectrum, appears to decrease with increasing molecular size. 5) The first reduction potential becomes less negative, but only slightly, whereas the first oxidation potential shows a marked shift to less positive values with increasing molecular size, indicating that the HOMO destabilizes significantly as the molecule becomes larger. 6) In 5), the extent of the HOMO destabilization with molecular size differs depending on the central metal, so metals producing smaller destabilization effects can allow larger macrocycles. Of the metals studied, the most effective is cobalt, and the practical size limit is represented by the Acs. 7) The IR spectra become simpler the larger the molecule, and the main bands were assigned by DFT calculations. 8) The trend in experimentally determined redox potentials and electronic absorption and MCD spectra were reasonably reproduced by MO calculations using the ZINDO/S Hamiltonian. 9) EPR data for several metallocomplexes are also reported.

Singlet oxygen quantum yields and photostability of planar binuclear phthalocyanines

“…But the wellknown NIR photosensitizer zinc naphthalocyanine Zn4 is significantly less stable. The decreased photostability of naphthalocyanines [31,32] and antracenocyanines is well-known and can be explained by the destabilization of HOMO which was estimated from calculations [31] and electrochemistry [14,32]). In contrast, upon annelation of two or more Pc units via a shared benzene ring, the HOMO-LUMO gap (responsible for E exc ) is reduced to a greater extent by LUMO stabilization [33,34] than by HOMO destabilization (see Fig.…”

“…One type of NIR-absorbing phthalocyanine analogs are well-known naphthalocyanines (Nc) [13,14] and anthracenocyanines (Ac) [14,15]. However, their stability is significantly reduced compared to Pcs.…”

Synthesis and Study of Physicochemical Properties of New Substituted Tetrathieno[2,3-b]porphyrazines

“…Metal-free 4 exhibits Q-band splitting ( Figure 1a), that can be attributed to the non-degenerated LUMO orbital. [14] In contrast, Q-bands in complexes 2, 3, 5 were not split ( Figure 1 and Table 1). This result is in accord with the literature data [15] and DFT calculations [14] for porphyrazines.…”

“…[14] In contrast, Q-bands in complexes 2, 3, 5 were not split ( Figure 1 and Table 1). This result is in accord with the literature data [15] and DFT calculations [14] for porphyrazines. The absence of Q-band splitting and the values of full width at half maximum (FWHM) for porphyrazine complexes in THF (Table 1.)…”

Sandwich-Type Lanthanide(III) Dinaphthalocyanine Complexes Possessing an Intensive Absorption in the Near IR Region: Synthesis and Investigation of Properties

“…[1][2][3][4] It is known that the widening of the conjugation system causes a considerable (up to 100 nm) bathochromic shift of the Q-band in the electronic absorption spectra of naphthalocyanines in comparison with the spectra of phthalocyanines. [5][6][7][8] An introduction of functional groups into naphthalocyanine ligands, a possibility of a central ion incorporation into the macrocycle, and an ability, similarly to phthalocyanines, to form double decker complexes allows one to vary their properties within a wide range.…”