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Title: Substantial Intramolecular Charge Transfer Induces Long Emission Wavelengths and Mega Stokes Shifts in 6-Aminocoumarins

Abstract

Coumarins are deployed in numerous bioimaging and biosensing applications. Among various coumarin derivatives, 6-aminocoumarins attract increasing attention for their red-shifted emissions, mega Stokes shifts, and significant solvatochromism. These spectral characteristics together with weak emission intensities have historically been ascribed to the formation of the twisted intramolecular charge transfer (TICT) state in 6-aminocoumarins. In this work, we demonstrate that it is actually substantial intramolecular charge transfer (ICT) that is responsible for these fluorescent properties. Based on this new understanding, we reanalyzed the sensing mechanism of a 6-aminocouarmin based fluorescent probe and obtained close agreement with experimental data. Lastly, our results lead to a deeper understanding of the photophysics of 6-aminocoumarins and will inspire the rational development of novel fluorescent probes.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]
  1. Univ. of Cambridge, Cambridge (United Kingdom); Singapore Univ. of Technology and Design (Singapore); Singapore-MIT Alliance for Research and Technology (SMART) (Singapore)
  2. Univ. of Cambridge, Cambridge (United Kingdom); STFC Rutherford Appleton Lab., Didcot (United Kingdom); Argonne National Lab. (ANL), Argonne, IL (United States)
  3. Chinese Academy of Sciences, Dalian (China)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1376720
Grant/Contract Number:
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 24; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Liu, Xiaogang, Cole, Jacqueline M., and Xu, Zhaochao. Substantial Intramolecular Charge Transfer Induces Long Emission Wavelengths and Mega Stokes Shifts in 6-Aminocoumarins. United States: N. p., 2017. Web. doi:10.1021/acs.jpcc.7b04176.
Liu, Xiaogang, Cole, Jacqueline M., & Xu, Zhaochao. Substantial Intramolecular Charge Transfer Induces Long Emission Wavelengths and Mega Stokes Shifts in 6-Aminocoumarins. United States. doi:10.1021/acs.jpcc.7b04176.
Liu, Xiaogang, Cole, Jacqueline M., and Xu, Zhaochao. 2017. "Substantial Intramolecular Charge Transfer Induces Long Emission Wavelengths and Mega Stokes Shifts in 6-Aminocoumarins". United States. doi:10.1021/acs.jpcc.7b04176.
@article{osti_1376720,
title = {Substantial Intramolecular Charge Transfer Induces Long Emission Wavelengths and Mega Stokes Shifts in 6-Aminocoumarins},
author = {Liu, Xiaogang and Cole, Jacqueline M. and Xu, Zhaochao},
abstractNote = {Coumarins are deployed in numerous bioimaging and biosensing applications. Among various coumarin derivatives, 6-aminocoumarins attract increasing attention for their red-shifted emissions, mega Stokes shifts, and significant solvatochromism. These spectral characteristics together with weak emission intensities have historically been ascribed to the formation of the twisted intramolecular charge transfer (TICT) state in 6-aminocoumarins. In this work, we demonstrate that it is actually substantial intramolecular charge transfer (ICT) that is responsible for these fluorescent properties. Based on this new understanding, we reanalyzed the sensing mechanism of a 6-aminocouarmin based fluorescent probe and obtained close agreement with experimental data. Lastly, our results lead to a deeper understanding of the photophysics of 6-aminocoumarins and will inspire the rational development of novel fluorescent probes.},
doi = {10.1021/acs.jpcc.7b04176},
journal = {Journal of Physical Chemistry. C},
number = 24,
volume = 121,
place = {United States},
year = 2017,
month = 6
}

Journal Article:
Free Publicly Available Full Text
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  • Photochemical and photophysical properties of phenylethynyldisilanes in MP (methylcyclohexane/isopentane, 3:1 v/v) have been studied by means of picosecond and nanosecond spectroscopy along with steady-state experiments. Intramolecular charge transfer in the excited singlet state of phenylethynyldisilanes occurs very rapidly (<10 ps) at both 77 and 294 K. This finding shows that internal rotation (or twisting) or solvation is not necessary for the intramolecular CT formation of phenylethynyldisilanes. The mechanism on the intramolecular CT from the /sup 1/(..pi..,..pi..*) state to the /sup 1/(2p..pi..,3d..pi..) CT state of the compounds is quite different from that of the usual TICT (twisted intramolecular charge transfer). Twomore » decay components (fast and slow) of the /sup 1/CT state are observed, which are ascribed to the intersystem crossing rates from /sup 1/CT to /sup 3/(..pi..,..pi..*), depending upon the molecular conformations of the /sup 1/CT state of phenylethynyldisilanes. The photochemical reaction to produce silacyclopropenes takes place effectively via the /sup 1/CT state at room temperature, but not in MP glass at 77 K.« less
  • A semiempirical MO study of the intramolecular charge transfer (CT) in the excited singlet states of dinaphthylamines has been carried out with the program systems MOPAC and ARGUS. The excited-state energies for various conformations of the molecules were obtained, in both the absence and the presence of a polarizable medium, by adding the transition energies calculated with the INDO I/S method to the ground-state energies calculated by means of the AM1 method. The CT state corresponds to a twisted geometry in which one naphthalene moiety is conjugated with the amino bridge, while the other moiety is perpendicular to the first.more » The gas-phase energy of this twisted intramolecular CT (TICT) state is only slightly greater than that of the lowest excited singlet (S[sub 1]) state of smaller dipole moment. In solvent of large dielectric constant, the TICT state is therefore predicted to be the lowest excited singlet state of the module. The computed oscillator strength of the absorption to the TICT state is much smaller than that to the lowest-energy excited state of an isolated molecule, so that the increase CT character of the S[sub 1] state in polar solvents is expected to lead to a decrease in the radiative decay rate of the state. These results are consistent with the experimental observation of a large fluorescence Stokes shift, and a reduction in the S[sub 1] radiative decay rate, of the compounds in polar solvents relative to nonpolar solvents. 14 refs., 9 figs., 4 tabs.« less
  • Time-resolved transient absorption spectra and time-resolved delayed emission spectra of dilute solutions of 1,1'-dinaphthylamine at room temperature demonstrate the formation of an intramolecular triplet excimer. Solvent polarity dependence of the spectral and temporal characteristics indicates that the formation of the intramolecular triplet excimer is facilitated by intermoiety charge-transfer interactions in the lowest excited singlet state of the molecule. 11 refs., 10 figs.
  • The time-resolved emission spectra of N-phenyl-2-naphthylamine reveal the formation of an intramolecular triplet exciplex in fluid solutions at room temperature. The exciplex formation involves transformation of the {open_quotes}noninteracting{close_quotes} conformation {sup 3}(M-X){sup *}-N, in which the excitation is largely localized on the naphthylamine (M-X) moiety, to the {open_quotes}interacting{close_quotes} conformation {sup 3}(M-X-N){sup *} with delocalized excitation. 6 refs., 8 figs.
  • Comparisons of the temporal characteristics of the transient absorption with those of the delayed fluorescence for dinaphthylmethanes and dinaphthyl ethers provide compelling kinetic evidence for the formation of intramolecular triplet excimers. 7 refs., 7 figs., 1 tab.