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Excited States of Porphyrin Macrocycles

  Articoli su Riviste JCR/ISI  (anno 2008)

Autori:  Moroni L., Gellini C., Salvi P.R., Marcelli A., Foggi P

Affiliazione Autori:  Univ Florence, Dipartimento Chim, I-50019 Florence, Italy; Univ Florence, Lab Europeo Spettroscopie Non Lineari LENS, I-50019 Florence, Italy; Univ Perugia, Dipartimento Chim, I-06123 Perugia, Italy; INOA CNR, I-50125 Florence, Italy

Riassunto:  S-1 -> S-n spectra of porphyrin, diprotonated porphyrin, and tetraoxaporphyrin dication have been measured in the energy range 2-3 eV above S-1 at room temperature in solution by means of transient absorption spectroscopy exciting with femtosecond pulses. Highly excited pi pi* states not active in the conventional S-0 -> S-n spectrum have been observed. The experimental data are discussed on the basis of the time dependent density functional theory taking advantage of large scale calculations of configuration interaction between singly excited configurations (DF/SCI). The DF/SCI calculation on porphyrin has allowed to assign g states active in the S-1 -> S-n. spectrum. Applying the same calculation method to tetraoxaporphyrin dication the S-0 -> S-n spectrum is reproduced relatively to the Q and B (Soret) bands as well as to the weaker E. bands at higher energy. According to our calculation the S-1 -> S-n. transient spectrum is related to states of g symmetry mainly arising from excitations between doubly degenerate pi and pi* orbitals such as 2e(g) - 4e(g). In the case of diprotonated porphyrin it is shown that the complex of the macrocycle with two trifluoroacetate anions plays a significant role for absorption. Charge transfer excitations from the anions to the macrocycle contribute to absorption above the Soret band, justifying the intensity enhancement of the S-0 -> S-n. spectrum with respect to the other two macrocyclic systems.

Volume n.:  112 (44)      Pagine da: 11044  a: 11051
Ulteriori informazioni:  The authors are grateful to Prof. E. Vogel (University of Koln, Germany) for the generous gift of a sample of tetraoxaporphyrin perchlorate. This work was supported by INSTM under the contract FIRB RBNE033KMA and by the European Community under the contract RIII-CT-2003-506350.
DOI: 10.1021/jp803249d

*Impact Factor della Rivista: (2008) 2.871   *Citazioni: 24
data tratti da "WEB OF SCIENCE" (marchio registrato di Thomson Reuters) ed aggiornati a:  19/05/2019

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