TY - JOUR
T1 - Solvent-induced configuration mixing and triplet excited-state inversion
T2 - Insights from transient absorption and transient dc photoconductivity measurements
AU - She, Chunxing
AU - Rachford, Aaron A.
AU - Wang, Xianghuai
AU - Goeb, Sébastien
AU - El-Ballouli, Ala'A O.
AU - Castellano, Felix N.
AU - Hupp, Joseph T.
PY - 2009
Y1 - 2009
N2 - Solvent-induced excited-state configuration mixing in a Pt(ii) diimine chromophore with phenylene ethynylene containing acetylide ligands, [Pt( tBu2bpy)(PE3)2] (1), was characterized by nanosecond transient absorption spectroscopy and transient dc photoconductivity (TDCP). The mixing is a result of closely spaced triplet charge transfer ( 3CT) and intraligand-localized (3IL) triplet energy levels that are finely tuned with solvent polarity as ascertained by their parent model chromophores [Pt(tBu2bpy)(PE1)2] (2) and [Pt(P2)(PE3)2] (3), respectively. The absorption difference spectrum of the mixed triplet state is dramatically different from those of the 3CT and 3IL state model chromophores. The 3CT, 3IL and configuration-mixed triplet states led to distinct TDCP signals. The TDCP response is of negative polarity for 3CT excited states but of positive polarity for 3IL excited states. TDCP transients for 1 in mixed solvents are a combination of signals from the 3IL and 3CT states, with the signal magnitude depending on the polarity of solvent composition. The fraction of 3CT state character in the configurationally mixed excited state was quantified by TDCP to be ∼0.24 in pure benzene, while it decreased to ∼0.05 in 20: 80 (v: v) benzene-CH2Cl2. The charge transfer fraction appears to increase slightly to ∼0.11 in the lower polarity 20: 80 n-hexane-CH 2Cl2 medium. TDCP is shown to be a useful tool for the identification of the lowest excited state in electrically neutral metal-organic chromophores.
AB - Solvent-induced excited-state configuration mixing in a Pt(ii) diimine chromophore with phenylene ethynylene containing acetylide ligands, [Pt( tBu2bpy)(PE3)2] (1), was characterized by nanosecond transient absorption spectroscopy and transient dc photoconductivity (TDCP). The mixing is a result of closely spaced triplet charge transfer ( 3CT) and intraligand-localized (3IL) triplet energy levels that are finely tuned with solvent polarity as ascertained by their parent model chromophores [Pt(tBu2bpy)(PE1)2] (2) and [Pt(P2)(PE3)2] (3), respectively. The absorption difference spectrum of the mixed triplet state is dramatically different from those of the 3CT and 3IL state model chromophores. The 3CT, 3IL and configuration-mixed triplet states led to distinct TDCP signals. The TDCP response is of negative polarity for 3CT excited states but of positive polarity for 3IL excited states. TDCP transients for 1 in mixed solvents are a combination of signals from the 3IL and 3CT states, with the signal magnitude depending on the polarity of solvent composition. The fraction of 3CT state character in the configurationally mixed excited state was quantified by TDCP to be ∼0.24 in pure benzene, while it decreased to ∼0.05 in 20: 80 (v: v) benzene-CH2Cl2. The charge transfer fraction appears to increase slightly to ∼0.11 in the lower polarity 20: 80 n-hexane-CH 2Cl2 medium. TDCP is shown to be a useful tool for the identification of the lowest excited state in electrically neutral metal-organic chromophores.
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U2 - 10.1039/b908977b
DO - 10.1039/b908977b
M3 - Article
C2 - 19774291
AN - SCOPUS:70349469399
SN - 1463-9076
VL - 11
SP - 8586
EP - 8591
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 38
ER -