TY - JOUR
T1 - Impact of Cyanine Conformational Restraint in the Near-Infrared Range
AU - Matikonda, Siddharth S.
AU - Hammersley, Gabrielle
AU - Kumari, Nikita
AU - Grabenhorst, Lennart
AU - Glembockyte, Viktorija
AU - Tinnefeld, Philip
AU - Ivanic, Joseph
AU - Levitus, Marcia
AU - Schnermann, Martin J.
N1 - Funding Information:
This work was supported by the Intramural Research Program of the National Institutes of Health, National Cancer Institute, Center for Cancer Research. M.J.S. thanks Dr. Joseph Barchi, NCI-CCR, for NMR assistance and Dr. James Kelley, NCI-CCR, for mass spectrometric analysis. Dr. Luke Lavis, Janelia Research Campus, Howard Hughes Medical Institute, is acknowledged for assistance with fluorescence quantum yield determination. This project has been funded in whole or in part with Federal funds from the National Cancer Institute, National Institutes of Health, under Contract No. HHSN261200800001E. M.L. acknowledges use of the UltraFast Laser Spectroscopy Facility at ASU. P.T. acknowledges support by the DFG (excellence cluster e-conversion). V.G. thanks the support of the Alexander von Humboldt Foundation.
Publisher Copyright:
© 2020 American Chemical Society.
PY - 2020/5/1
Y1 - 2020/5/1
N2 - Appending conformationally restraining ring systems to the cyanine chromophore creates exceptionally bright fluorophores in the visible range. Here, we report the application of this strategy in the near-infrared range through the preparation of the first restrained heptamethine indocyanine. Time-resolved absorption spectroscopy and fluorescence correlation spectroscopy verify that, unlike the corresponding parent unrestrained variant, the restrained molecule is not subject to photoisomerization. Notably, however, the room-temperature emission efficiency and the fluorescence lifetime of the restrained cyanine are not extended relative to the parent cyanine, even in viscous solvents. Thus, in contrast to prior reports, the photoisomerization of heptamethine cyanines does not contribute significantly to the excited-state chemistry of these molecules. We also find that the fluorescence lifetime of the restrained heptamethine cyanine is temperature-insensitive and significantly extended at moderately elevated temperatures relative to the parent cyanine. Finally, computational studies have been used to evaluate the impact of the conformational restraint on atomic and orbital structure across the cyanine series. These studies clarify the role of photoisomerization in the heptamethine cyanine scaffold and demonstrate the dramatic effect of restraint on the temperature sensitivity of these dyes.
AB - Appending conformationally restraining ring systems to the cyanine chromophore creates exceptionally bright fluorophores in the visible range. Here, we report the application of this strategy in the near-infrared range through the preparation of the first restrained heptamethine indocyanine. Time-resolved absorption spectroscopy and fluorescence correlation spectroscopy verify that, unlike the corresponding parent unrestrained variant, the restrained molecule is not subject to photoisomerization. Notably, however, the room-temperature emission efficiency and the fluorescence lifetime of the restrained cyanine are not extended relative to the parent cyanine, even in viscous solvents. Thus, in contrast to prior reports, the photoisomerization of heptamethine cyanines does not contribute significantly to the excited-state chemistry of these molecules. We also find that the fluorescence lifetime of the restrained heptamethine cyanine is temperature-insensitive and significantly extended at moderately elevated temperatures relative to the parent cyanine. Finally, computational studies have been used to evaluate the impact of the conformational restraint on atomic and orbital structure across the cyanine series. These studies clarify the role of photoisomerization in the heptamethine cyanine scaffold and demonstrate the dramatic effect of restraint on the temperature sensitivity of these dyes.
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U2 - 10.1021/acs.joc.0c00236
DO - 10.1021/acs.joc.0c00236
M3 - Article
AN - SCOPUS:85083158794
SN - 0022-3263
VL - 85
SP - 5907
EP - 5915
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
IS - 9
ER -