TY - JOUR
T1 - Ultrafast stimulated emission and structural dynamics in nickel porphyrins
AU - Zhang, Xiaoyi
AU - Wasinger, Erik C.
AU - Muresan, Ana Z.
AU - Attenkofer, Klaus
AU - Jennings, Guy
AU - Lindsey, Jonathan S.
AU - Chen, Lin X
PY - 2007/11/22
Y1 - 2007/11/22
N2 - The excited-state structural dynamics of nickel(II)tetrakis(2,4,6- trimethylphenyl)porphyrin (NiTMP) and nickel(II)tetrakis(tridec-7-yl)porphyrin (NiSWTP) in a toluene solution were investigated via ultrafast transient optical absorption spectroscopy. An ultrashort stimulated emission between 620 and 670 nm from the S 1 state was observed in both nickel porphyrins only when this state was directly generated via Q-band excitation, whereas such a stimulated emission was absent under B (Soret)-band excitation. Because the stimulated emission in the spectral region occurs only from the S 1 state, this photoexcitation-wavelength-dependent behavior of Ni(II) porphyrins is attributed to a faster intersystem crossing from the S 2 state than the internal conversion S 2 - S 1. The dynamics of the excited-state pathways involving the (π, π*) and (d, d) states varies with the meso-substituted peripheral groups, which is attributed to the nickel porphyrin macrocycle distortion from a planar configuration. Evidence for intramolecular vibrational relaxation within 2 ps and vibrational cooling in 6 - 20 ps of a (d, d) excited state has been established for NiTMP and NiSWTP. Finally, the lifetimes of the vibrationally relaxed (d, d) state also depend on the nature of the peripheral groups, decreasing from 200 ps for NiTMP to 100 ps for the bulkier NiSWTP.
AB - The excited-state structural dynamics of nickel(II)tetrakis(2,4,6- trimethylphenyl)porphyrin (NiTMP) and nickel(II)tetrakis(tridec-7-yl)porphyrin (NiSWTP) in a toluene solution were investigated via ultrafast transient optical absorption spectroscopy. An ultrashort stimulated emission between 620 and 670 nm from the S 1 state was observed in both nickel porphyrins only when this state was directly generated via Q-band excitation, whereas such a stimulated emission was absent under B (Soret)-band excitation. Because the stimulated emission in the spectral region occurs only from the S 1 state, this photoexcitation-wavelength-dependent behavior of Ni(II) porphyrins is attributed to a faster intersystem crossing from the S 2 state than the internal conversion S 2 - S 1. The dynamics of the excited-state pathways involving the (π, π*) and (d, d) states varies with the meso-substituted peripheral groups, which is attributed to the nickel porphyrin macrocycle distortion from a planar configuration. Evidence for intramolecular vibrational relaxation within 2 ps and vibrational cooling in 6 - 20 ps of a (d, d) excited state has been established for NiTMP and NiSWTP. Finally, the lifetimes of the vibrationally relaxed (d, d) state also depend on the nature of the peripheral groups, decreasing from 200 ps for NiTMP to 100 ps for the bulkier NiSWTP.
UR - http://www.scopus.com/inward/record.url?scp=37049036855&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=37049036855&partnerID=8YFLogxK
U2 - 10.1021/jp0751763
DO - 10.1021/jp0751763
M3 - Article
C2 - 17966996
AN - SCOPUS:37049036855
SN - 1089-5639
VL - 111
SP - 11736
EP - 11742
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 46
ER -