Singlet and triplet excited states of emissive, conjugated bis(porphyrin) compounds probed by optical and EPR spectroscopic methods

Renée Shediac, Mike H B Gray, H. Tetsuo Uyeda, Robert C. Johnson, Joseph T Hupp, Paul J. Angiolillo, Michael J. Therien

Research output: Contribution to journalArticle

129 Citations (Scopus)

Abstract

The nature of the singlet and triplet excited states of a series of meso-to-meso ethyne-linked bis(porphyrin) compounds was probed by electronic absorption, polarized pump - probe fluorescence, electron paramagnetic resonance (EPR), electroabsorption (Stark), and transient triplet - triplet absorption spectroscopic methods, Pump - probe fluorescence anisotropy experiments show that the presence of meso-ethynyl substituents drives a reorientation of orthogonal x- and y-polarized singlet excited states in the macrocycle frame of reference with respect to that evinced for conventional free-base porphyrin chromophores. Analogous experiments in conjugated bis(porphyrin) species bis[(5,5',-10,20-bis[3,5-(di-tert -butyl)phenyl]porphinato)zinc(II)]ethyne, 5-[10,20-bis[3,5-(di-tert-butyl)phenyl]porphinato)zinc(II)]-5'- [10',20'-bis[3,5-(di-tert-butyl)phenyl]porphyryl]ethyne, and bis[5,5',-10,20-bis[3,5-(di-tert-butyl)phenyl]porphyryl]ethyne demonstrate substantial energetic splittings of the x- and y-polarized S1 states. The magnitude of this energetic gap results in the complete suppression of population exchange between excited states having orthogonal polarizations on the time scale of these measurements, and gives rise to singly degenerate emitting states polarized exclusively along the axis defined by the ethyne moiety. Stark spectroscopic experiments show that the electronically symmetric meso-to-meso ethyne-bridged bis[(porphinato)zinc(II)] complex exhibits changes in dipole moment with respect to the ground state in its respective x-polarized S2 and S1 states. The EPR spectra of the low-lying photoexcited triplet excited states of these conjugated bis(porphyrin) compounds and their ethyne-substituted porphyrinic building blocks show an evolution in the |D| and |E| ZFS parameters with augmented conjugation consistent with a progressing oblate-to-prolate spin transition that causes the direction of largest dipolar interaction to align along the vector defined by the conjugated ethyne moiety. Conjugated arrays based on meso-ethyne elaborated porphyrin and (porphinato)zinc(II) precursors thus constitute an unusual class of oligomeric porphyrin species in that once a threshold level of conjugation is reached, the optical and magnetic principal axis systems become coincident.

Original languageEnglish
Pages (from-to)7017-7033
Number of pages17
JournalJournal of the American Chemical Society
Volume122
Issue number29
DOIs
Publication statusPublished - Jul 26 2000

Fingerprint

Acetylene
Porphyrins
Electron Spin Resonance Spectroscopy
Excited states
Paramagnetic resonance
Zinc
Fluorescence
Pumps
Experiments
Dipole moment
Chromophores
Phosmet
Ground state
Anisotropy
Fluorescence Polarization
Polarization

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Singlet and triplet excited states of emissive, conjugated bis(porphyrin) compounds probed by optical and EPR spectroscopic methods. / Shediac, Renée; Gray, Mike H B; Tetsuo Uyeda, H.; Johnson, Robert C.; Hupp, Joseph T; Angiolillo, Paul J.; Therien, Michael J.

In: Journal of the American Chemical Society, Vol. 122, No. 29, 26.07.2000, p. 7017-7033.

Research output: Contribution to journalArticle

Shediac, Renée ; Gray, Mike H B ; Tetsuo Uyeda, H. ; Johnson, Robert C. ; Hupp, Joseph T ; Angiolillo, Paul J. ; Therien, Michael J. / Singlet and triplet excited states of emissive, conjugated bis(porphyrin) compounds probed by optical and EPR spectroscopic methods. In: Journal of the American Chemical Society. 2000 ; Vol. 122, No. 29. pp. 7017-7033.
@article{d203a6278b6b4320b98c1c3c728e9dae,
title = "Singlet and triplet excited states of emissive, conjugated bis(porphyrin) compounds probed by optical and EPR spectroscopic methods",
abstract = "The nature of the singlet and triplet excited states of a series of meso-to-meso ethyne-linked bis(porphyrin) compounds was probed by electronic absorption, polarized pump - probe fluorescence, electron paramagnetic resonance (EPR), electroabsorption (Stark), and transient triplet - triplet absorption spectroscopic methods, Pump - probe fluorescence anisotropy experiments show that the presence of meso-ethynyl substituents drives a reorientation of orthogonal x- and y-polarized singlet excited states in the macrocycle frame of reference with respect to that evinced for conventional free-base porphyrin chromophores. Analogous experiments in conjugated bis(porphyrin) species bis[(5,5',-10,20-bis[3,5-(di-tert -butyl)phenyl]porphinato)zinc(II)]ethyne, 5-[10,20-bis[3,5-(di-tert-butyl)phenyl]porphinato)zinc(II)]-5'- [10',20'-bis[3,5-(di-tert-butyl)phenyl]porphyryl]ethyne, and bis[5,5',-10,20-bis[3,5-(di-tert-butyl)phenyl]porphyryl]ethyne demonstrate substantial energetic splittings of the x- and y-polarized S1 states. The magnitude of this energetic gap results in the complete suppression of population exchange between excited states having orthogonal polarizations on the time scale of these measurements, and gives rise to singly degenerate emitting states polarized exclusively along the axis defined by the ethyne moiety. Stark spectroscopic experiments show that the electronically symmetric meso-to-meso ethyne-bridged bis[(porphinato)zinc(II)] complex exhibits changes in dipole moment with respect to the ground state in its respective x-polarized S2 and S1 states. The EPR spectra of the low-lying photoexcited triplet excited states of these conjugated bis(porphyrin) compounds and their ethyne-substituted porphyrinic building blocks show an evolution in the |D| and |E| ZFS parameters with augmented conjugation consistent with a progressing oblate-to-prolate spin transition that causes the direction of largest dipolar interaction to align along the vector defined by the conjugated ethyne moiety. Conjugated arrays based on meso-ethyne elaborated porphyrin and (porphinato)zinc(II) precursors thus constitute an unusual class of oligomeric porphyrin species in that once a threshold level of conjugation is reached, the optical and magnetic principal axis systems become coincident.",
author = "Ren{\'e}e Shediac and Gray, {Mike H B} and {Tetsuo Uyeda}, H. and Johnson, {Robert C.} and Hupp, {Joseph T} and Angiolillo, {Paul J.} and Therien, {Michael J.}",
year = "2000",
month = "7",
day = "26",
doi = "10.1021/ja9939587",
language = "English",
volume = "122",
pages = "7017--7033",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "29",

}

TY - JOUR

T1 - Singlet and triplet excited states of emissive, conjugated bis(porphyrin) compounds probed by optical and EPR spectroscopic methods

AU - Shediac, Renée

AU - Gray, Mike H B

AU - Tetsuo Uyeda, H.

AU - Johnson, Robert C.

AU - Hupp, Joseph T

AU - Angiolillo, Paul J.

AU - Therien, Michael J.

PY - 2000/7/26

Y1 - 2000/7/26

N2 - The nature of the singlet and triplet excited states of a series of meso-to-meso ethyne-linked bis(porphyrin) compounds was probed by electronic absorption, polarized pump - probe fluorescence, electron paramagnetic resonance (EPR), electroabsorption (Stark), and transient triplet - triplet absorption spectroscopic methods, Pump - probe fluorescence anisotropy experiments show that the presence of meso-ethynyl substituents drives a reorientation of orthogonal x- and y-polarized singlet excited states in the macrocycle frame of reference with respect to that evinced for conventional free-base porphyrin chromophores. Analogous experiments in conjugated bis(porphyrin) species bis[(5,5',-10,20-bis[3,5-(di-tert -butyl)phenyl]porphinato)zinc(II)]ethyne, 5-[10,20-bis[3,5-(di-tert-butyl)phenyl]porphinato)zinc(II)]-5'- [10',20'-bis[3,5-(di-tert-butyl)phenyl]porphyryl]ethyne, and bis[5,5',-10,20-bis[3,5-(di-tert-butyl)phenyl]porphyryl]ethyne demonstrate substantial energetic splittings of the x- and y-polarized S1 states. The magnitude of this energetic gap results in the complete suppression of population exchange between excited states having orthogonal polarizations on the time scale of these measurements, and gives rise to singly degenerate emitting states polarized exclusively along the axis defined by the ethyne moiety. Stark spectroscopic experiments show that the electronically symmetric meso-to-meso ethyne-bridged bis[(porphinato)zinc(II)] complex exhibits changes in dipole moment with respect to the ground state in its respective x-polarized S2 and S1 states. The EPR spectra of the low-lying photoexcited triplet excited states of these conjugated bis(porphyrin) compounds and their ethyne-substituted porphyrinic building blocks show an evolution in the |D| and |E| ZFS parameters with augmented conjugation consistent with a progressing oblate-to-prolate spin transition that causes the direction of largest dipolar interaction to align along the vector defined by the conjugated ethyne moiety. Conjugated arrays based on meso-ethyne elaborated porphyrin and (porphinato)zinc(II) precursors thus constitute an unusual class of oligomeric porphyrin species in that once a threshold level of conjugation is reached, the optical and magnetic principal axis systems become coincident.

AB - The nature of the singlet and triplet excited states of a series of meso-to-meso ethyne-linked bis(porphyrin) compounds was probed by electronic absorption, polarized pump - probe fluorescence, electron paramagnetic resonance (EPR), electroabsorption (Stark), and transient triplet - triplet absorption spectroscopic methods, Pump - probe fluorescence anisotropy experiments show that the presence of meso-ethynyl substituents drives a reorientation of orthogonal x- and y-polarized singlet excited states in the macrocycle frame of reference with respect to that evinced for conventional free-base porphyrin chromophores. Analogous experiments in conjugated bis(porphyrin) species bis[(5,5',-10,20-bis[3,5-(di-tert -butyl)phenyl]porphinato)zinc(II)]ethyne, 5-[10,20-bis[3,5-(di-tert-butyl)phenyl]porphinato)zinc(II)]-5'- [10',20'-bis[3,5-(di-tert-butyl)phenyl]porphyryl]ethyne, and bis[5,5',-10,20-bis[3,5-(di-tert-butyl)phenyl]porphyryl]ethyne demonstrate substantial energetic splittings of the x- and y-polarized S1 states. The magnitude of this energetic gap results in the complete suppression of population exchange between excited states having orthogonal polarizations on the time scale of these measurements, and gives rise to singly degenerate emitting states polarized exclusively along the axis defined by the ethyne moiety. Stark spectroscopic experiments show that the electronically symmetric meso-to-meso ethyne-bridged bis[(porphinato)zinc(II)] complex exhibits changes in dipole moment with respect to the ground state in its respective x-polarized S2 and S1 states. The EPR spectra of the low-lying photoexcited triplet excited states of these conjugated bis(porphyrin) compounds and their ethyne-substituted porphyrinic building blocks show an evolution in the |D| and |E| ZFS parameters with augmented conjugation consistent with a progressing oblate-to-prolate spin transition that causes the direction of largest dipolar interaction to align along the vector defined by the conjugated ethyne moiety. Conjugated arrays based on meso-ethyne elaborated porphyrin and (porphinato)zinc(II) precursors thus constitute an unusual class of oligomeric porphyrin species in that once a threshold level of conjugation is reached, the optical and magnetic principal axis systems become coincident.

UR - http://www.scopus.com/inward/record.url?scp=0034718076&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0034718076&partnerID=8YFLogxK

U2 - 10.1021/ja9939587

DO - 10.1021/ja9939587

M3 - Article

AN - SCOPUS:0034718076

VL - 122

SP - 7017

EP - 7033

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 29

ER -