The effect of “on/off” molecular switching on the photophysical and photochemical properties of axially calixarene substituted activatable silicon(iv)phthalocyanine photosensitizers

Abstract

Silicon(iv) phthalocyanines ( and ) bearing two calixarene groups as axial ligands were synthesized. Surprisingly, both phthalocyanines were obtained as two different isomers ( and ) depending on the distance between calixarene benzene groups and the phthalocyanine ring. DFT and TD-DFT computations were performed to model plausible structures of these isomers and to simulate electronic absorption spectra. These isomers converted into each other depending on the polarity of the used solvent, temperature and light irradiation. The photophysical and photochemical properties of each isomer were investigated in dimethylsulfoxide (DMSO) for the determination of photodynamic therapy (PDT) activities of these compounds. The more blue-shifted isomers ( and ) showed higher fluorescence quantum yields and singlet oxygen generation compared to more red-shifted counterparts ( and ). This behavior is extremely important for developing activatable photosensitizers for cancer treatment by PDT. Although these photosensitizers produce lower singlet oxygen in normal cells, they produce higher singlet oxygen (six times higher for ) in cancer cells since these photosensitizers converted to more blue-shifted isomers by using light irradiation.

Investigation of photochemical and photophysical properties of novel silicon(IV) phthalocyanines and their $\mu $-oxo dimers

“…The methyl protons were observed at high field at around 0.73-0.52 ppm for 4a and 0.54-0.31 ppm for 4b due to the magnetic anisotropy effect of the Pc ring. 19 The mass spectra of the silicon(IV) Pcs (3a, 3b and 4a, 4b) also confirmed the proposed structures of (Figure S9). Furthermore, the mass spectra of the dimers (4a, 4b) show that they did not consist of a trimer.…”

“…The methyl protons were observed at around 0.85 ppm, which is higher field than expected due to the magnetic anisotropy effect of the Pc ring. 19 In the 1 H NMR spectra of dimeric silicon(IV) Pc derivatives (4a and 4b), the Si-OH protons were observed at around -2.42 ppm. The aromatic protons on the Pc ring were observed as two sets between 8.75-8.07 and 7.92-7.44 ppm for 4a and between 9.11-8.33 and 8.28-7.97 ppm for 4b, integrating 24 protons.…”

“…In the 1 H NMR spectra of the monomeric silicon(IV) phthalocyanine derivatives (3a and 3b), the Si-OH protons were observed at -2.05 ppm for 3a and -2.10 ppm for 3b due to the magnetic anisotropy of the Pc core. 19 The aromatic protons of Pcs were observed between 8.73 and 8.10 ppm for 3a and between 8.75 and 8.07 ppm for 3b, integrating a total of twelve protons. The aliphatic CH 2 protons were observed at three different regions at around 3.40, 1.75, and 1.25-1.45 ppm due to their diverse chemical environment and their proximity to the Pc rings.…”

“…In the 1 H NMR spectra of the monomeric silicon(IV) phthalocyanine derivatives (3a and 3b), the Si-OH protons were observed at -2.05 ppm for 3a and -2.10 ppm for 3b due to the magnetic anisotropy of the Pc core. 19 The aromatic protons of Pcs were observed between ( Figure S9). Furthermore, the mass spectra of the dimers (4a, 4b) show that they did not consist of a trimer.…”

Synthesis of nonperipherally tetra-[5-(diethylamino)-2-formylphenoxy] substituted metallophthalocyanines and their electrochemistry

“…They have extended πconjugation system and different type of central metal [2]. In addition, their unique electronic and chemical properties, physical and optical properties, as well as their chemical flexibility of phthalocyanines allow preparation of variety of related structures and diverse applications ranging from industrial to biological areas [3,4]. Phthalocyanines have been used in different areas such as photodynamic therapy [5,6], nonlinear optical materials [7], electrochemical sensors [8,9], biosensors [10], solar cells [11,12], light-emitting decives [13], liquid crystals [14], electrocatalyts [15], electropolymerization [16,17].…”