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Excited state intramolecular proton transfer in hydroxyanthraquinones: Toward predicting fading of organic red colorants in art

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Science Advances  06 Sep 2019:
Vol. 5, no. 9, eaaw5227
DOI: 10.1126/sciadv.aaw5227
  • Fig. 1 The molecules of this study.

    Molecules having a 1,4-OH motif are above the images, and those without 1,4-OH motif are below them. Isomers within the LE ZPE corrected structure (labeled I) (~25 kJ/mol) are also shown with their relative energy values (kJ/mol) with respect to the LE form. Central to this figure is the common madder root and its primary chromophores alizarin and purpurin. Photo credit: Jacob Berenbeim, UCSB

  • Fig. 2 Picosecond 2C-R2PI spectra of each HAQ in this study (OPG + 213 nm).

    Intensities have been normalized.

  • Fig. 3 Results of picosecond pump-probe spectroscopy.

    (A) Pump-probe lifetime as measured at the origin transition (red bars) and at excess energy (black bars) arranged in order of decreasing measured lifetimes. The excess energy transition used is noted next to the black bars. (B) Pump-probe traces of the molecules with the longest and shortest measured excited state lifetime, 1,2,4-HAQ and 1,2-HAQ, respectively, plotted over 500 ps. The pump-probe data are fit to a curve (blue trace), which is the sum of a single exponential decay (green trace) convolved with a Gaussian component (red trace) representative of our instrument response function.

  • Fig. 4 IR hole burning spectra.

    Spectra were taken in mode I of 1,2,4-HAQ, 1,4-HAQ, and 1,8-HAQ probed at their origin R2PI transition. a.u., arbitrary units.

  • Fig. 5 Potential-energy energy profiles of 1-HAQ.

    Profiles shown are of the S0 state (black circles), the S1(ππ*) state (blue squares), and the S1(nπ*) state (red diamonds) of the 1-HAQ molecule as a function of the torsional reaction path (A and C) and the hydrogen transfer reaction path (B). Full lines (full symbols): Energy profiles of reaction paths determined in the same electronic state. Dashed lines (empty symbols) represent ground-state energy calculated for the geometry optimized in the given excited state nπ*(red) or ππ* (blue). Purple rectangles highlight the nπ* and ππ* intersections.

  • Fig. 6 PESs of 1,4-HAQ.

    (A) Minimum PES of the S0 state, (B) the S1(ππ*) singlet excited state, and (C) the S1(nπ*) singlet excited state of the 1,4-HAQ molecule as a function of the hydrogen transfer reaction path as a function of two coordinates: R(O1….H) and R(O4…H). (D) Schematic indication of the structures at the four combinations of minimum and maximum R values. The location of each tautomer on the PES is also labeled.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaaw5227/DC1

    Fig. S1. Picosecond pump-probe spectra.

    Fig. S2. Nanosecond pump-probe spectra.

    Fig. S3. IR hole burning spectra in mode II with the burn laser set to 3090 cm−1.

    Fig. S4. Hole burning spectra in mode I.

    Table S1. Calculated properties of 1-HAQ and 1,4-HAQ.

    Table S2. Emission properties of 1-HAQ.

    Table S3. Emission properties of 1,4-HAQ.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Picosecond pump-probe spectra.
    • Fig. S2. Nanosecond pump-probe spectra.
    • Fig. S3. IR hole burning spectra in mode II with the burn laser set to 3090 cm−1.
    • Fig. S4. Hole burning spectra in mode I.
    • Table S1. Calculated properties of 1-HAQ and 1,4-HAQ.
    • Table S2. Emission properties of 1-HAQ.
    • Table S3. Emission properties of 1,4-HAQ.

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    Files in this Data Supplement:

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