title: Bis(porphyrin)-anthraquinone triads: synthesis, spectroscopy, and photochemistry.
abstract: Molecular triads based on bis(porphyrin)-anthraquinone having azomethine bridge at the pyrrole-β position have been designed and synthesized. Both free-base AQ-(H2)2 and zinc AQ-(Zn)2 triads are characterized by elemental analysis, MALDI-MS, (1)H NMR, UV-visible, and fluorescence spectroscopy (steady-state and time-resolved) as well as electrochemical method. The absorption spectra of both Soret and Q-bands of the triads are red-shifted by 12-20 nm with respect to their monomer units. The study supported by theoretical calculations manifests that there exists a negligible electronic communication in the ground state between the donor porphyrin and acceptor anthraquinone of these triads. However, interestingly, both the triads exhibit significant fluorescence emission quenching (51-92%) of the porphyrin emission compared to their monomeric units. The emission quenching is attributed to the excited-state intramolecular photoinduced electron transfer from porphyrins to anthraquinone. The electron-transfer rates (kET) of these triads are found in the range 1.0 × 10(8) to 7.7 × 10(9) s(-1) and are found to be solvent dependent.
authors.affiliation: Inorganic & Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad 500007, A.P., India. giribabu@iict.res.in
authors.forename: L
authors.initials: L
authors.lastname: Giribabu
authors.forename: P Silviya
authors.initials: PS
authors.lastname: Reeta
authors.forename: Ravi Kumar
authors.initials: RK
authors.lastname: Kanaparthi
authors.forename: Malladi
authors.initials: M
authors.lastname: Srikanth
authors.forename: Y
authors.initials: Y
authors.lastname: Soujanya
mesh_terms: D000880:Anthraquinones / Q000138:chemical synthesis / Q000737:chemistry* / Q000528:radiation effects; D004563:Electrochemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010777:Photochemistry; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry* / Q000528:radiation effects; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000880:Anthraquinones; D011166:Porphyrins