Ultrafast intersystem crossing and spin dynamics of zinc meso-tetraphenylporphyrin covalently bound to stable radicals

Michael T. Colvin, Amanda L. Smeigh, Emilie M. Giacobbe, Sarah M Mickley Conron, Annie Butler Ricks, Michael R Wasielewski

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Tert-Butylphenylnitroxide (BPNO) and α,γ- bisdiphenylene-β-phenylallyl (BDPA) stable radicals are each attached to zinc meso-tetraphenylporphyrin (ZnTPP) at a fixed distance using one of the ZnTPP phenyl groups. BPNO and BDPA are oriented para (1 and 3, respectively) or meta (2 and 4, respectively) relative to the porphyrin macrocycle. Following photoexcitation of 1-4, transient optical absorption spectroscopy is used to observe excited state quenching of 1ZnTPP by the radicals and time-resolved electron paramagnetic resonance (TREPR) spectroscopy is used to monitor the spin dynamics of the paramagnetic product states. The presence of BPNO or BDPA accelerates the intersystem crossing rate of 1ZnTPP about 10- to 500-fold in 1-4 depending on the structure compared to that of 1ZnTPP itself. In addition, the lifetime of 3ZnTPP in 1 is shorter than that of 3ZnTPP itself as a result of enhanced intersystem crossing (EISC) from 3ZnTPP to the ground state. The TREPR spectra of the three unpaired spins produced within 1 and 2 show spin-polarized excited doublet (D1) and quartet (Q) states and subsequent formation of a spin-polarized ground state radical (D 0). All three signals are absorptive for 1 and emissive for 2. Polarization inversion of the Q state is observed on a tens of nanoseconds time scale in 2, while no polarization inversion is observed for 1. The lack of polarization inversion in 1 is attributed to the short lifetime of the doublet-quartet manifold as a result of the very large exchange interaction. The TREPR spectra of 3 and 4 show ground state radical polarization at X-band (9.5 GHz) at room temperature, but not at 85 K, and similarly no polarization is observed at W-band (94 GHz). No evidence of excited doublet or quartet states is observed, indicating that the exchange interaction is both weak and temperature dependent. These results show that although ultrafast EISC produces 3ZnTPP within 1-4, the magnitude of the exchange interactions between the three relevant spins in the resulting 3ZnTPP-BPNO and 3ZnTPP-BDPA systems dramatically alters their spin dynamics.

Original languageEnglish
Pages (from-to)7538-7549
Number of pages12
JournalJournal of Physical Chemistry A
Volume115
Issue number26
DOIs
Publication statusPublished - Jul 7 2011

Fingerprint

Spin dynamics
spin dynamics
Zinc
zinc
Polarization
Exchange interactions
Ground state
Paramagnetic resonance
polarization
electron paramagnetic resonance
inversions
ground state
life (durability)
Photoexcitation
Porphyrins
interactions
superhigh frequencies
photoexcitation
Absorption spectroscopy
Excited states

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Ultrafast intersystem crossing and spin dynamics of zinc meso-tetraphenylporphyrin covalently bound to stable radicals. / Colvin, Michael T.; Smeigh, Amanda L.; Giacobbe, Emilie M.; Conron, Sarah M Mickley; Ricks, Annie Butler; Wasielewski, Michael R.

In: Journal of Physical Chemistry A, Vol. 115, No. 26, 07.07.2011, p. 7538-7549.

Research output: Contribution to journalArticle

Colvin, Michael T. ; Smeigh, Amanda L. ; Giacobbe, Emilie M. ; Conron, Sarah M Mickley ; Ricks, Annie Butler ; Wasielewski, Michael R. / Ultrafast intersystem crossing and spin dynamics of zinc meso-tetraphenylporphyrin covalently bound to stable radicals. In: Journal of Physical Chemistry A. 2011 ; Vol. 115, No. 26. pp. 7538-7549.
@article{11e3498d01704b48b7b2af3bda7304bf,
title = "Ultrafast intersystem crossing and spin dynamics of zinc meso-tetraphenylporphyrin covalently bound to stable radicals",
abstract = "Tert-Butylphenylnitroxide (BPNO•) and α,γ- bisdiphenylene-β-phenylallyl (BDPA•) stable radicals are each attached to zinc meso-tetraphenylporphyrin (ZnTPP) at a fixed distance using one of the ZnTPP phenyl groups. BPNO• and BDPA • are oriented para (1 and 3, respectively) or meta (2 and 4, respectively) relative to the porphyrin macrocycle. Following photoexcitation of 1-4, transient optical absorption spectroscopy is used to observe excited state quenching of 1ZnTPP by the radicals and time-resolved electron paramagnetic resonance (TREPR) spectroscopy is used to monitor the spin dynamics of the paramagnetic product states. The presence of BPNO• or BDPA• accelerates the intersystem crossing rate of 1ZnTPP about 10- to 500-fold in 1-4 depending on the structure compared to that of 1ZnTPP itself. In addition, the lifetime of 3ZnTPP in 1 is shorter than that of 3ZnTPP itself as a result of enhanced intersystem crossing (EISC) from 3ZnTPP to the ground state. The TREPR spectra of the three unpaired spins produced within 1 and 2 show spin-polarized excited doublet (D1) and quartet (Q) states and subsequent formation of a spin-polarized ground state radical (D 0). All three signals are absorptive for 1 and emissive for 2. Polarization inversion of the Q state is observed on a tens of nanoseconds time scale in 2, while no polarization inversion is observed for 1. The lack of polarization inversion in 1 is attributed to the short lifetime of the doublet-quartet manifold as a result of the very large exchange interaction. The TREPR spectra of 3 and 4 show ground state radical polarization at X-band (9.5 GHz) at room temperature, but not at 85 K, and similarly no polarization is observed at W-band (94 GHz). No evidence of excited doublet or quartet states is observed, indicating that the exchange interaction is both weak and temperature dependent. These results show that although ultrafast EISC produces 3ZnTPP within 1-4, the magnitude of the exchange interactions between the three relevant spins in the resulting 3ZnTPP-BPNO • and 3ZnTPP-BDPA• systems dramatically alters their spin dynamics.",
author = "Colvin, {Michael T.} and Smeigh, {Amanda L.} and Giacobbe, {Emilie M.} and Conron, {Sarah M Mickley} and Ricks, {Annie Butler} and Wasielewski, {Michael R}",
year = "2011",
month = "7",
day = "7",
doi = "10.1021/jp2021006",
language = "English",
volume = "115",
pages = "7538--7549",
journal = "Journal of Physical Chemistry A",
issn = "1089-5639",
publisher = "American Chemical Society",
number = "26",

}

TY - JOUR

T1 - Ultrafast intersystem crossing and spin dynamics of zinc meso-tetraphenylporphyrin covalently bound to stable radicals

AU - Colvin, Michael T.

AU - Smeigh, Amanda L.

AU - Giacobbe, Emilie M.

AU - Conron, Sarah M Mickley

AU - Ricks, Annie Butler

AU - Wasielewski, Michael R

PY - 2011/7/7

Y1 - 2011/7/7

N2 - Tert-Butylphenylnitroxide (BPNO•) and α,γ- bisdiphenylene-β-phenylallyl (BDPA•) stable radicals are each attached to zinc meso-tetraphenylporphyrin (ZnTPP) at a fixed distance using one of the ZnTPP phenyl groups. BPNO• and BDPA • are oriented para (1 and 3, respectively) or meta (2 and 4, respectively) relative to the porphyrin macrocycle. Following photoexcitation of 1-4, transient optical absorption spectroscopy is used to observe excited state quenching of 1ZnTPP by the radicals and time-resolved electron paramagnetic resonance (TREPR) spectroscopy is used to monitor the spin dynamics of the paramagnetic product states. The presence of BPNO• or BDPA• accelerates the intersystem crossing rate of 1ZnTPP about 10- to 500-fold in 1-4 depending on the structure compared to that of 1ZnTPP itself. In addition, the lifetime of 3ZnTPP in 1 is shorter than that of 3ZnTPP itself as a result of enhanced intersystem crossing (EISC) from 3ZnTPP to the ground state. The TREPR spectra of the three unpaired spins produced within 1 and 2 show spin-polarized excited doublet (D1) and quartet (Q) states and subsequent formation of a spin-polarized ground state radical (D 0). All three signals are absorptive for 1 and emissive for 2. Polarization inversion of the Q state is observed on a tens of nanoseconds time scale in 2, while no polarization inversion is observed for 1. The lack of polarization inversion in 1 is attributed to the short lifetime of the doublet-quartet manifold as a result of the very large exchange interaction. The TREPR spectra of 3 and 4 show ground state radical polarization at X-band (9.5 GHz) at room temperature, but not at 85 K, and similarly no polarization is observed at W-band (94 GHz). No evidence of excited doublet or quartet states is observed, indicating that the exchange interaction is both weak and temperature dependent. These results show that although ultrafast EISC produces 3ZnTPP within 1-4, the magnitude of the exchange interactions between the three relevant spins in the resulting 3ZnTPP-BPNO • and 3ZnTPP-BDPA• systems dramatically alters their spin dynamics.

AB - Tert-Butylphenylnitroxide (BPNO•) and α,γ- bisdiphenylene-β-phenylallyl (BDPA•) stable radicals are each attached to zinc meso-tetraphenylporphyrin (ZnTPP) at a fixed distance using one of the ZnTPP phenyl groups. BPNO• and BDPA • are oriented para (1 and 3, respectively) or meta (2 and 4, respectively) relative to the porphyrin macrocycle. Following photoexcitation of 1-4, transient optical absorption spectroscopy is used to observe excited state quenching of 1ZnTPP by the radicals and time-resolved electron paramagnetic resonance (TREPR) spectroscopy is used to monitor the spin dynamics of the paramagnetic product states. The presence of BPNO• or BDPA• accelerates the intersystem crossing rate of 1ZnTPP about 10- to 500-fold in 1-4 depending on the structure compared to that of 1ZnTPP itself. In addition, the lifetime of 3ZnTPP in 1 is shorter than that of 3ZnTPP itself as a result of enhanced intersystem crossing (EISC) from 3ZnTPP to the ground state. The TREPR spectra of the three unpaired spins produced within 1 and 2 show spin-polarized excited doublet (D1) and quartet (Q) states and subsequent formation of a spin-polarized ground state radical (D 0). All three signals are absorptive for 1 and emissive for 2. Polarization inversion of the Q state is observed on a tens of nanoseconds time scale in 2, while no polarization inversion is observed for 1. The lack of polarization inversion in 1 is attributed to the short lifetime of the doublet-quartet manifold as a result of the very large exchange interaction. The TREPR spectra of 3 and 4 show ground state radical polarization at X-band (9.5 GHz) at room temperature, but not at 85 K, and similarly no polarization is observed at W-band (94 GHz). No evidence of excited doublet or quartet states is observed, indicating that the exchange interaction is both weak and temperature dependent. These results show that although ultrafast EISC produces 3ZnTPP within 1-4, the magnitude of the exchange interactions between the three relevant spins in the resulting 3ZnTPP-BPNO • and 3ZnTPP-BDPA• systems dramatically alters their spin dynamics.

UR - http://www.scopus.com/inward/record.url?scp=79959795186&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79959795186&partnerID=8YFLogxK

U2 - 10.1021/jp2021006

DO - 10.1021/jp2021006

M3 - Article

C2 - 21630656

AN - SCOPUS:79959795186

VL - 115

SP - 7538

EP - 7549

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 26

ER -