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Title: Controlling the excited-state dynamics of low band gap, near-infrared absorbers via proquinoidal unit electronic structural modulation

While the influence of proquinoidal character upon the linear absorption spectrum of low optical bandgap π-conjugated polymers and molecules is well understood, its impact upon excited-state relaxation pathways and dynamics remains obscure. We report the syntheses, electronic structural properties, and excited-state dynamics of a series of model highly conjugated near-infrared (NIR)-absorbing chromophores based on a (porphinato)metal(II)-proquinoidal spacer-(porphinato)metal(II) (PM-Sp-PM) structural motif. A combination of excited-state dynamical studies and time-dependent density functional theory calculations: (i) points to the cardinal role that excited-state configuration interaction (CI) plays in determining the magnitudes of S 1 → S 0 radiative (k r), S 1 → T 1 intersystem crossing (k ISC), and S 1 → S 0 internal conversion (k IC) rate constants in these PM-Sp-PM chromophores, and (ii) suggests that a primary determinant of CI magnitude derives from the energetic alignment of the PM and Sp fragment LUMOs (ΔE L). These insights not only enable steering of excited-state relaxation dynamics of high oscillator strength NIR absorbers to realize either substantial fluorescence or long-lived triplets (τ$$_ {T_1}$$ > μs) generated at unit quantum yield (Φ ISC = 100%), but also crafting of those having counter-intuitive properties: for example, while (porphinato)platinum compounds are well known to generate non-emissive triplet states (Φ ISC = 100%) upon optical excitation at ambient temperature, diminishing the extent of excited-state CI in these systems realizes long-wavelength absorbing heavy-metal fluorophores. In conclusion, this work highlights approaches to: (i) modulate low-lying singlet excited-state lifetime over the picosecond-to-nanosecond time domain, (ii) achieve NIR fluorescence with quantum yields up to 25%, (iii) tune the magnitude of S 1–T 1 ISC rate constant from 10 9 to 10 12 s -1 and (iv) realize T 1-state lifetimes that range from ~0.1 to several μs, for these model PM-Sp-PM chromophores, and renders new insights to evolve bespoke photophysical properties for low optical bandgap π-conjugated polymers and molecules based on proquinoidal conjugation motifs.
Authors:
 [1] ; ORCiD logo [1] ;  [1] ;  [1] ;  [1] ;  [1] ; ORCiD logo [1] ; ORCiD logo [1]
  1. Duke Univ., Durham, NC (United States). Dept. of Chemistry, French Family Science Center
Publication Date:
Grant/Contract Number:
SC0001517; GM048043
Type:
Accepted Manuscript
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 8; Journal Issue: 9; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry
Research Org:
Duke Univ., Durham, NC (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Institutes of Health (NIH)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1426479

Bai, Yusong, Rawson, Jeff, Roget, Sean A., Olivier, Jean-Hubert, Lin, Jiaxing, Zhang, Peng, Beratan, David N., and Therien, Michael J.. Controlling the excited-state dynamics of low band gap, near-infrared absorbers via proquinoidal unit electronic structural modulation. United States: N. p., Web. doi:10.1039/c7sc02150j.
Bai, Yusong, Rawson, Jeff, Roget, Sean A., Olivier, Jean-Hubert, Lin, Jiaxing, Zhang, Peng, Beratan, David N., & Therien, Michael J.. Controlling the excited-state dynamics of low band gap, near-infrared absorbers via proquinoidal unit electronic structural modulation. United States. doi:10.1039/c7sc02150j.
Bai, Yusong, Rawson, Jeff, Roget, Sean A., Olivier, Jean-Hubert, Lin, Jiaxing, Zhang, Peng, Beratan, David N., and Therien, Michael J.. 2017. "Controlling the excited-state dynamics of low band gap, near-infrared absorbers via proquinoidal unit electronic structural modulation". United States. doi:10.1039/c7sc02150j. https://www.osti.gov/servlets/purl/1426479.
@article{osti_1426479,
title = {Controlling the excited-state dynamics of low band gap, near-infrared absorbers via proquinoidal unit electronic structural modulation},
author = {Bai, Yusong and Rawson, Jeff and Roget, Sean A. and Olivier, Jean-Hubert and Lin, Jiaxing and Zhang, Peng and Beratan, David N. and Therien, Michael J.},
abstractNote = {While the influence of proquinoidal character upon the linear absorption spectrum of low optical bandgap π-conjugated polymers and molecules is well understood, its impact upon excited-state relaxation pathways and dynamics remains obscure. We report the syntheses, electronic structural properties, and excited-state dynamics of a series of model highly conjugated near-infrared (NIR)-absorbing chromophores based on a (porphinato)metal(II)-proquinoidal spacer-(porphinato)metal(II) (PM-Sp-PM) structural motif. A combination of excited-state dynamical studies and time-dependent density functional theory calculations: (i) points to the cardinal role that excited-state configuration interaction (CI) plays in determining the magnitudes of S1 → S0 radiative (kr), S1 → T1 intersystem crossing (kISC), and S1 → S0 internal conversion (kIC) rate constants in these PM-Sp-PM chromophores, and (ii) suggests that a primary determinant of CI magnitude derives from the energetic alignment of the PM and Sp fragment LUMOs (ΔEL). These insights not only enable steering of excited-state relaxation dynamics of high oscillator strength NIR absorbers to realize either substantial fluorescence or long-lived triplets (τ$_ {T_1}$ > μs) generated at unit quantum yield (ΦISC = 100%), but also crafting of those having counter-intuitive properties: for example, while (porphinato)platinum compounds are well known to generate non-emissive triplet states (ΦISC = 100%) upon optical excitation at ambient temperature, diminishing the extent of excited-state CI in these systems realizes long-wavelength absorbing heavy-metal fluorophores. In conclusion, this work highlights approaches to: (i) modulate low-lying singlet excited-state lifetime over the picosecond-to-nanosecond time domain, (ii) achieve NIR fluorescence with quantum yields up to 25%, (iii) tune the magnitude of S1–T1 ISC rate constant from 109 to 1012 s-1 and (iv) realize T1-state lifetimes that range from ~0.1 to several μs, for these model PM-Sp-PM chromophores, and renders new insights to evolve bespoke photophysical properties for low optical bandgap π-conjugated polymers and molecules based on proquinoidal conjugation motifs.},
doi = {10.1039/c7sc02150j},
journal = {Chemical Science},
number = 9,
volume = 8,
place = {United States},
year = {2017},
month = {6}
}

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In vivo near-infrared fluorescence imaging
journal, October 2003

Contracted Gaussian basis sets for molecular calculations. I. Second row atoms, Z=11–18
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