Tunable Excited-State Properties and Dynamics as a Function of Pt-Pt Distance in Pyrazolate-Bridged Pt(II) Dimers

Samantha E. Brown-Xu, Matthew S J Kelley, Kelly A. Fransted, Arnab Chakraborty, George C Schatz, Felix N. Castellano, Lin X. Chen

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)543-550
Number of pages8
JournalJournal of Physical Chemistry A
Volume120
Issue number4
DOIs
Publication statusPublished - Feb 4 2016

Fingerprint

Excited states
Dimers
dimers
Ligands
ligands
Platinum
excitation
platinum
Metals
Density functional theory
Charge transfer
charge transfer
metals
density functional theory
Relaxation processes
Chromophores
Absorption spectroscopy
Molecular structure
chromophores
time constant

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Tunable Excited-State Properties and Dynamics as a Function of Pt-Pt Distance in Pyrazolate-Bridged Pt(II) Dimers. / Brown-Xu, Samantha E.; Kelley, Matthew S J; Fransted, Kelly A.; Chakraborty, Arnab; Schatz, George C; Castellano, Felix N.; Chen, Lin X.

In: Journal of Physical Chemistry A, Vol. 120, No. 4, 04.02.2016, p. 543-550.

Research output: Contribution to journalArticle

Brown-Xu, Samantha E. ; Kelley, Matthew S J ; Fransted, Kelly A. ; Chakraborty, Arnab ; Schatz, George C ; Castellano, Felix N. ; Chen, Lin X. / Tunable Excited-State Properties and Dynamics as a Function of Pt-Pt Distance in Pyrazolate-Bridged Pt(II) Dimers. In: Journal of Physical Chemistry A. 2016 ; Vol. 120, No. 4. pp. 543-550.
@article{9d871a54375e48d3acf7f66bc79230f4,
title = "Tunable Excited-State Properties and Dynamics as a Function of Pt-Pt Distance in Pyrazolate-Bridged Pt(II) Dimers",
abstract = "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.",
author = "Brown-Xu, {Samantha E.} and Kelley, {Matthew S J} and Fransted, {Kelly A.} and Arnab Chakraborty and Schatz, {George C} and Castellano, {Felix N.} and Chen, {Lin X.}",
year = "2016",
month = "2",
day = "4",
doi = "10.1021/acs.jpca.5b11233",
language = "English",
volume = "120",
pages = "543--550",
journal = "Journal of Physical Chemistry A",
issn = "1089-5639",
publisher = "American Chemical Society",
number = "4",

}

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.

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

VL - 120

SP - 543

EP - 550

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 4

ER -