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Mitsui M, Takakura Y, Hirata K, Niihori Y, Fujiwara Y, Kobayashi K. Excited-State Symmetry Breaking in a Multiple Multipolar Chromophore Probed by Single-Molecule Fluorescence Imaging and Spectroscopy. J Phys Chem B 2021; 125:9950-9959. [PMID: 34455782 DOI: 10.1021/acs.jpcb.1c04915] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Excited-state symmetry breaking (ESB) has attracted much attention because it is often observed in symmetric multipolar chromophores designed as two-photon absorption/emission materials. Herein, we report an ensemble and single-molecule fluorescence imaging and spectroscopy investigation of ESB in hexakis[4-(p-dioctylaminostyryl)phenylethynyl]benzene(DB6), a two-photon absorber possessing a C6-symmetric π-D6 structure (π = hexaethynylbenzene, D = (p-dioctylaminostyryl)phenyl group) consisting of three equivalent D-π-D moieties. Ensemble and single-molecule measurements and theoretical calculations revealed that DB6 undergoes a photoabsorption process with two orthogonal transition dipole moments, whereas it fluoresces with a single transition dipole moment after one- or two-step ESB upon photoexcitation, depending on the environmental polarity. In nonpolar solvents and polymer films, one of the three D-π-D sites becomes planar, and the excited state is localized on this moiety: a [Dδ+-πδ--Dδ+]* quadrupolar state is formed. In polar solvents, the symmetry is further broken within the planarized D-π-D moiety, and the excited state is localized on one of the two D-π sites; i.e., a D-[πδ--Dδ+]* dipolar state is generated. Hence, DB6 can behave like a multichromophore with multiple emission sites in the molecule, which was demonstrated by stepwise photobleaching under photon antibunching conditions.
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Affiliation(s)
- Masaaki Mitsui
- Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebukuro, Toshima-ku, Tokyo 171-8501, Japan
| | - Yasushi Takakura
- Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebukuro, Toshima-ku, Tokyo 171-8501, Japan
| | - Kazuya Hirata
- Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebukuro, Toshima-ku, Tokyo 171-8501, Japan
| | - Yoshiki Niihori
- Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebukuro, Toshima-ku, Tokyo 171-8501, Japan
| | - Yutaka Fujiwara
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
| | - Kenji Kobayashi
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
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Lynch PG, Richards H, Wustholz KL. Unraveling the Excited-State Dynamics of Eosin Y Photosensitizers Using Single-Molecule Spectroscopy. J Phys Chem A 2019; 123:2592-2600. [PMID: 30835475 DOI: 10.1021/acs.jpca.9b00409] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The intersystem crossing and dispersive electron-transfer dynamics of eosin Y (EY) photosensitizers are probed using single-molecule microscopy. The blinking dynamics of EY on glass are quantified by constructing cumulative distribution functions of emissive ("on") and nonemissive ("off") events. Maximum likelihood estimation (MLE) and goodness-of-fit tests based on the Kolmogorov-Smirnov (KS) statistic are used to establish the best fit to the blinking data and differentiate among competitive photophysical processes. The on-time probability distributions for EY in N2 and air are power-law distributed after ∼1 s, with fit parameters that are significantly modified upon exposure to oxygen. By extending the statistically principled MLE/KS approach to include an onset time for log-normal behavior, we demonstrate that the off-time distribution for EY in N2 is best fit to a combination of exponential and log-normal functions. The corresponding distribution for EY in air is best fit to a log-normal function alone. Furthermore, power law and log-normal distributions are observed for an individual molecule in air, consistent with dynamic fluctuations in the rate constant for dark-state population and depopulation. These observations support the interpretation that dispersive electron transfer (i.e., the Albery model) from the first excited singlet state (S1) of EY to trap states on glass is predominately responsible for blinking in oxic conditions. In anoxic environment, both triplet-state blinking and dispersive electron transfer from S1 and the excited triplet state (T1) contribute to the excited-state dynamics of EY.
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Affiliation(s)
- Pauline G Lynch
- College of William and Mary , Department of Chemistry , P.O. Box 8795, Williamsburg , Virginia 23187 , United States
| | - Huw Richards
- College of William and Mary , Department of Chemistry , P.O. Box 8795, Williamsburg , Virginia 23187 , United States
| | - Kristin L Wustholz
- College of William and Mary , Department of Chemistry , P.O. Box 8795, Williamsburg , Virginia 23187 , United States
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