Relationship between Symmetry of Porphyrinic π-Conjugated Systems and Singlet Oxygen (¹Δ_g) Yields:  Low-Symmetry Tetraazaporphyrin Derivatives

Abstract

We have investigated the excited-state properties and singlet oxygen ((1)Delta(g)) generation mechanism in phthalocyanines (4M; M = H(2), Mg, or Zn) and in low-symmetry metal-free, magnesium, and zinc tetraazaporphyrins (TAPs), that is, monobenzo-substituted (1M), adjacently dibenzo-substituted (2AdM), oppositely dibenzo-substituted (2OpM), and tribenzo-substituted (3M) TAP derivatives, whose pi conjugated systems were altered by fusing benzo rings. The S(1)(x) and S(1)(y) states (these lowest excited singlet states are degenerate in D(4)(h) symmetry) split in the low-symmetry TAP derivatives. The excited-state energies were quantitatively determined from the electronic absorption spectra. The lowest excited triplet (T(1)(x)) energies were also determined from phosphorescence spectra, while the second lowest excited triplet (T(1)(y)) states were evaluated by using the energy splitting between the T(1)(x) and T(1)(y) states previously reported (Miwa, H.; Ishii, K.; Kobayashi, N. Chem. Eur. J. 2004, 10, 4422-4435). The singlet oxygen quantum yields (Phi(Delta)) are strongly dependent on the pi conjugated system. In particular, while the Phi(Delta) value of 2AdH(2) is smallest in our system, that of 2OpH(2), an isomer of 2AdH(2), is larger than that of 4Zn, in contrast to the heavy atom effect. The relationship between the molecular structure and Phi(Delta) values can be transformed into a relationship between the S(1)(x) --> T(1)(y) intersystem crossing rate constant (k(ISC)) and the energy difference between the S(1)(x) and T(1)(y) states (DeltaE(S)(x)(T)(y)). In each of the Zn, Mg, and metal-free compounds, the Phi(Delta)/tau(F) values (tau(F): fluorescence lifetime), which are related to the k(ISC) values, are proportional to exp(-DeltaE(S)(x)(T)(y)), indicating that singlet oxygen ((1)Delta(g)) is produced via the T(1)(y) state and that the S(1)(x) --> T(1)(y) ISC process follows the energy-gap law. From the viewpoint of photodynamic therapy, our methodology, where the Phi(Delta) value can be controlled by changing the symmetry of pi conjugated systems without heavy elements, appears useful for preparing novel photosensitizers.

Synthesis, Separation and UV/Vis Spectroscopy of Pyrazino‐quinoxalino‐porphyrazine Macrocycles

“…This approach in the synthesis of unsymmetrical Pc and related compounds is sometimes called a statistical condensation. [30] Different selective strategies [30][31][32] leading to only AAAB (the sub-phthalocyanine approach [33] or the polymer support approach [34] ), ABAB [35][36][37] or AABB [35,38,39] derivatives have also been developed.…”

Synthesis and characterization of cobalt(II), nickel(II) and copper(II)-based potential photosensitizers: Evaluation of their DNA binding profile, cleavage and photocytotoxicity

“…The complex 1 was found to be the most efficient singlet oxygen generator from the series of complexes studied. It has been proved by Ishii et al that there is a relationship between the symmetry of the aromatic π-conjugated systems and singlet oxygen yields [108]. It seems advantageous that the metal based photosensitizers studied possess values of singlet oxygen generation quantum yields comparable to that of photosensitizers used commercially in PDT.…”

Unsymmetrical Porphyrazines Based on 3,6-Dioctyloxyphthalonitrile and 5,6-Diphenyl-2,3-dicyanopyrazine and Their Complexes with Copper. Synthesis and Spectral Properties

“…измерены на спек-трофотометре Helios Zeta при концентрациях ~5•10 -6 моль/л, ИК спектры -на спектрофотометре Avatar 360 FT-IR в области 400-4000 см Несимметричные порфиразины (3)(4)(5). В кипящий раствор гексан-1-олята лития в гексан-1-оле, приготовленный растворением 0.1 г лития в 30 мл безводного гексан-1-ола, вносили 0.34 г (1 ммоль) соединения 1, выдерживали 15 мин, добавляли 0.56 г (2 ммоль) соединения 2, выдерживали еще 2 ч и отгоняли 20 мл спирта.…”

“…В силу наличия у них выраженных дипольных моментов эти соединения представляют несомненный практиче-ский интерес для использования в оптических техно-логиях, [1][2][3] наличие функциональных групп различной природы определяет возможность использования этих соединений в медицине, в частности, для фотодинами-ческой терапии онкологических заболеваний. [4][5][6][7] Для синтеза таких порфиразинов наиболее часто исполь-зуется метод совместной конденсации двух различных о-динитрилов. [8][9][10][11] В результате обычно образуется смесь всех возможных порфиразинов, которые, в соответствии с общепринятой классификацией, подразделяются на типы: А 4 , А 3 В, ААВВ, АВАВ, АВ 3 и В 4 , где А и В -раз-личные периферийные фрагменты молекулы порфира-зина.…”