TY - JOUR
T1 - Tunable Excited-State Properties and Dynamics as a Function of Pt-Pt Distance in Pyrazolate-Bridged Pt(II) Dimers
AU - Brown-Xu, Samantha E.
AU - Kelley, Matthew S.J.
AU - Fransted, Kelly A.
AU - Chakraborty, Arnab
AU - Schatz, George C.
AU - Castellano, Felix N.
AU - Chen, Lin X.
N1 - Funding Information:
This work has been supported by funding from the National Science Foundation (CHE-1363007 to L.X.C. and CHE-1362942 to F.N.C.). The computational work is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. M.S.K. would like to acknowledge his NDSEG fellowship sponsored by the Air Force Office of Scientific Research.
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/2/4
Y1 - 2016/2/4
N2 - The influence of molecular structure on excited-state properties and dynamics of a series of cyclometalated platinum dimers was investigated through a combined experimental and theoretical approach using femtosecond transient absorption (fs TA) spectroscopy and density functional theory (DFT) calculations. The molecules have the general formula [Pt(ppy)(μ-R2pz)]2, where ppy = 2-phenylpyridine, pz = pyrazolate, and R = H, Me, Ph, or tBu, and are strongly photoluminescent at room temperature. The distance between the platinum centers in this A-frame geometry can be varied depending on the steric bulk of the bridging pyrazolate ligands that exert structural constraints and compress the Pt-Pt distance. At large Pt-Pt distances there is little interaction between the subunits, and the chromophore behaves similar to a monomer with excited states described as mixtures of ligand-centered and metal-to-ligand charge transfer (LC/MLCT) transitions. When the Pt(II) centers are brought closer together with bulky bridging ligands, they interact through their dz2 orbitals and the S1 and T1 states are best characterized as metal-metal-to-ligand charge transfer (MMLCT) in character. The results of the femtoseconds TA experiments reveal that intersystem crossing (ISC) occurs on ultrafast time scales (τS1 < 200 fs), while there are two relaxation processes occurring within the triplet manifold, τ1 = 0.5-3.2 ps and τ2 = 20-70 ps; the longer time constants correspond to the presence of bulkier bridging ligands. DFT calculations illustrate that the Pt-Pt distances further contract in the T1 3MMLCT states; therefore, slower relaxation may be related to a larger structural reorganization. Subsequent investigations using faster time resolution are planned to measure the ISC process as well as to identify any potential coherent interaction(s) between the platinum centers that may occur.
AB - The influence of molecular structure on excited-state properties and dynamics of a series of cyclometalated platinum dimers was investigated through a combined experimental and theoretical approach using femtosecond transient absorption (fs TA) spectroscopy and density functional theory (DFT) calculations. The molecules have the general formula [Pt(ppy)(μ-R2pz)]2, where ppy = 2-phenylpyridine, pz = pyrazolate, and R = H, Me, Ph, or tBu, and are strongly photoluminescent at room temperature. The distance between the platinum centers in this A-frame geometry can be varied depending on the steric bulk of the bridging pyrazolate ligands that exert structural constraints and compress the Pt-Pt distance. At large Pt-Pt distances there is little interaction between the subunits, and the chromophore behaves similar to a monomer with excited states described as mixtures of ligand-centered and metal-to-ligand charge transfer (LC/MLCT) transitions. When the Pt(II) centers are brought closer together with bulky bridging ligands, they interact through their dz2 orbitals and the S1 and T1 states are best characterized as metal-metal-to-ligand charge transfer (MMLCT) in character. The results of the femtoseconds TA experiments reveal that intersystem crossing (ISC) occurs on ultrafast time scales (τS1 < 200 fs), while there are two relaxation processes occurring within the triplet manifold, τ1 = 0.5-3.2 ps and τ2 = 20-70 ps; the longer time constants correspond to the presence of bulkier bridging ligands. DFT calculations illustrate that the Pt-Pt distances further contract in the T1 3MMLCT states; therefore, slower relaxation may be related to a larger structural reorganization. Subsequent investigations using faster time resolution are planned to measure the ISC process as well as to identify any potential coherent interaction(s) between the platinum centers that may occur.
UR - http://www.scopus.com/inward/record.url?scp=84957060153&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84957060153&partnerID=8YFLogxK
U2 - 10.1021/acs.jpca.5b11233
DO - 10.1021/acs.jpca.5b11233
M3 - Article
C2 - 26759897
AN - SCOPUS:84957060153
VL - 120
SP - 543
EP - 550
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
SN - 1089-5639
IS - 4
ER -