TY - JOUR
T1 - Photophysics of lanthanide triple decker porphyrin sandwich complexes
AU - Wittmer, Lisa L.
AU - Holten, Dewey
PY - 1996/1/11
Y1 - 1996/1/11
N2 - Ground state and time resolved excited state optical absorption spectra and luminescence spectra are reported for La2(OEP)3, Eu2(OEP)3, and Ce2(OEP)3 (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinate). The porphyrin macrocycles in these molecules are strongly coupled due to their mean separation of ≤3.5 Å. The triple deckers show many optical properties analogous to those found for double decker porphyrin sandwich complexes, including features not exhibited by porphyrin monomers. Following excitation, the lowest 1(π,π*) state of La2(OEP)3 decays in ∼10 ps predominantly to the phosphorescent 3(π,π*) state, which lives for ∼10 μs. The lowest 1(π,π*) state of Eu2(OEP)3 also decays rapidly and with high yield to the lowest 3(π,π*) state, which has a rather short lifetime of 630 ps. The lack of luminescence from Eu2(OEP)3 is ascribed to deactivation of the 3(π,π*) state through one or more low-energy ligand-field states of the metal ion. Ce2(OEP)3 is also nonluminescent. Unlike La2(OEP)3 and Eu2(OEP)3, the 1(π,π*) lifetime of 7 ps for Ce2(OEP)3 largely reflects deactivation within the singlet manifold. The decay of 1(π,π*) to the ground state likely involves low-lying (f,f) states, although a charge transfer state may play a role. The small (∼20%) population of 3(π,π*) that forms from 1(π,π*) also decays rapidly (τ ∼ 300 ps), again via ligand-field states of the metal ions. These combined results further demonstrate the importance of (i) π-π interactions in defining the electronic properties of chromophores brought within van der Waals distance and (ii) metal-centered excited states in determining the relaxation rates and pathways following photoexcitation of tetrapyrrole complexes.
AB - Ground state and time resolved excited state optical absorption spectra and luminescence spectra are reported for La2(OEP)3, Eu2(OEP)3, and Ce2(OEP)3 (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinate). The porphyrin macrocycles in these molecules are strongly coupled due to their mean separation of ≤3.5 Å. The triple deckers show many optical properties analogous to those found for double decker porphyrin sandwich complexes, including features not exhibited by porphyrin monomers. Following excitation, the lowest 1(π,π*) state of La2(OEP)3 decays in ∼10 ps predominantly to the phosphorescent 3(π,π*) state, which lives for ∼10 μs. The lowest 1(π,π*) state of Eu2(OEP)3 also decays rapidly and with high yield to the lowest 3(π,π*) state, which has a rather short lifetime of 630 ps. The lack of luminescence from Eu2(OEP)3 is ascribed to deactivation of the 3(π,π*) state through one or more low-energy ligand-field states of the metal ion. Ce2(OEP)3 is also nonluminescent. Unlike La2(OEP)3 and Eu2(OEP)3, the 1(π,π*) lifetime of 7 ps for Ce2(OEP)3 largely reflects deactivation within the singlet manifold. The decay of 1(π,π*) to the ground state likely involves low-lying (f,f) states, although a charge transfer state may play a role. The small (∼20%) population of 3(π,π*) that forms from 1(π,π*) also decays rapidly (τ ∼ 300 ps), again via ligand-field states of the metal ions. These combined results further demonstrate the importance of (i) π-π interactions in defining the electronic properties of chromophores brought within van der Waals distance and (ii) metal-centered excited states in determining the relaxation rates and pathways following photoexcitation of tetrapyrrole complexes.
UR - https://www.scopus.com/pages/publications/0029679227
U2 - 10.1021/jp952614+
DO - 10.1021/jp952614+
M3 - Article
AN - SCOPUS:0029679227
SN - 0022-3654
VL - 100
SP - 860
EP - 868
JO - Journal of Physical Chemistry
JF - Journal of Physical Chemistry
IS - 2
ER -