Formation, photophysics, and photochemistry of cadmium(II) complexes with 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin and its octabromo derivative: The effects of bromination and the axial hydroxo ligand

详细信息    查看全文

• 作者：Zsolt Valicsek^a ; ^{valicsek@vegic.uni-pannon.hu} ; Ottó ; Horvá ; th^a ; ^{otto@vegic.uni-pannon.hu} ; Gyö ; rgy Lendvay^a ; ^b ; ^{lendvay@chemres.hu} ; Ilijana Kika&#x161 ; ^c ; ^{ilijana.kikas@gmail.com} ; Irena &#x160 ; korić ; ^c ; ^{iskoric@fkit.hr}
• 关键词：Water-soluble porphyrin ; Out-of-plane ; Cadmium(II) ion ; Photochemistry ; Bromination ; Charge transfer
• 刊名：Journal of Photochemistry and Photobiology A: Chemistry
• 出版年：2011
• 出版时间：5 February 2011
• 年：2011
• 卷：218
• 期：1
• 页码：143-155
• 全文大小：1012 K

文摘

In slightly alkaline solution (pH 8) Cd(II) ion and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H₂P⁴⁻) form a kinetically labile complex (HOCdP⁵⁻), in which the metal center is located out of the ligand plane, due to the effects of the axial hydroxo ligand and the relatively large radius of Cd²⁺. Both acidification and irradiation at the Soret-band can result in the dissociation of the axial ligand, reducing the out-of-plane distance of the metal center and the distortion of the macrocycle (CdP⁴⁻). Besides, irradiation of both types of metalloporphyrins promotes an irreversible ligand-to-metal charge transfer leading to the oxidative degradation of the coordinated porphyrin at both the Soret- and the Q-bands. Under the same conditions, in the case of the octabromo derivative of this water-soluble porphyrin (H₂BrP⁴⁻), the distorted structure accelerates the formation of the corresponding complex with cadmium(II) compared to its reaction with the parent, unbrominated ligand. The structure of this porphyrin (HOCdBrP⁵⁻), similarly to the free base and CdBrP⁴⁻ (formed via acidification of irradiation of HOCdBrP⁵⁻), strongly distorted by the Br substituents significantly affects the characteristic features of the absorption and emission spectra, red-shifting the position of the main bands of these porphyrins compared to those of the unbrominated species. Also the emission quantum yields and lifetimes are dramatically diminished by bromination. Deviating from the unbrominated species, photodegradation of the brominated derivatives proved to be very oxygen sensitive. Besides, CdBrP⁴⁻ is transformed into a new porphyrin derivative upon both Soret- and Q-band irradiation. DFT calculations of the geometrical structures and the absorption bands show good correlations with the observed photophysical and photochemical properties, due to the drastic distortions of the macrocyclic ligand.