Relaxation properties of porphyrin, diprotonated porphyrin, and isoelectronic tetraoxaporphyrin dication in the S-2 state
Anno: 2007
Autori: Marcelli A., Foggi P., Moroni L., Gellini C., Salvi PR., Badovinac I.J.
Affiliazione autori: Laboratorio Europeo di Spettroscopie non Lineari (LENS), Universita´ di Firenze, Via N. Carrara 1, 50019 Sesto Fiorentino, Firenze, Italy;
Dipartimento di Chimica, Universita´ di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy;
Dipartimento di Chimica, Universita´ di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy;
Faculty of Arts and Sciences, Physics Department, University of Rijeka, Omladinska 14, Rijeka, Croatia;
CNR – Istituto Nazionale di Ottica Applicata, Largo E. Fermi 6, 50125 Firenze, Italy
Abstract: The fluorescence spectra of unsubstituted porphyrin (H2P), diprotonated porphyrin (H4P2+), and isoelectronic tetraoxaporphyrin dication (TOxP(2+)) have been measured in solution at room temperature. The S-2 -> S-0 fluorescence has been observed, much more intense for TOxP(2+) than for H4P2+ and H2P. In the TOxP(2+) case, the S-2 -> S-0 fluorescence spectrum is remarkably sharp and shows an excellent mirror symmetry with respect to S-0 -> S-2 absorption. On the contrary, the spectra of H4P2+ and H2P are shifted and more extended with respect to the absorption counterparts. The differences have been attributed primarily to the change of the equilibrium geometry upon excitation, larger in H2P and H4P2+ than in TOxP(2+) and in the case of H4P2+ to the nonplanar conformation of the macrocycle. Also the S-1 -> S-0 spectra of H2P, H4P2+, and TOxP(2+) have been measured and more qualitatively discussed. The S-1 and S-2 fluorescence decays have been observed for H4P2+ and TOxP(2+) exciting with ultrashort pulses. The S-2 lifetime of TOxP(2+) is of the order of the temporal resolution of our experimental apparatus, whereas that of H4P2+ is shorter. The S-2 -> S-0 quantum yield of TOxP(2+) has been estimated to be 0.035, similar to 3 orders of magnitude higher than that of H4P2+. It is proposed on the basis of ab initio model calculations that excited states of the H4P2+(CF3COO-)(2) complex with charge-transfer character are responsible of the increased extension of the S-2 -> S-0 spectrum with respect to that of H2P.
Giornale/Rivista: JOURNAL OF PHYSICAL CHEMISTRY A
Volume: 111 (12) Da Pagina: 2276 A: 2282
Parole chiavi: Charge transfer; Conformations; Fluorescence; Fluorescence spectroscopy; Relaxation processes, Diprotonated porphyrin; Fluorescence decays; Nonplanar conformation, Porphyrins, porphyrin; proton, article; chemical structure; chemistry; electron; photochemistry; spectroscopy; time, Electrons; Models, Molecular; Molecular Structure; Photochemistry; Porphyrins; Protons; Spectrum Analysis; Time FactorsDOI: 10.1021/jp0686846Citazioni: 26dati da “WEB OF SCIENCE” (of Thomson Reuters) aggiornati al: 2024-04-28Riferimenti tratti da Isi Web of Knowledge: (solo abbonati) Link per visualizzare la scheda su IsiWeb: Clicca quiLink per visualizzare la citazioni su IsiWeb: Clicca qui