| 1. |
- Li, Xiaoxin, et al.
(författare)
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Enhanced S-2 Fluorescence from a Free-Base Tetraphenylporphyrin Surface-Mounted Metal Organic Framework
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 122:41, s. 23321-23328
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Tidskriftsartikel (refereegranskat)abstract
- The ultrafast transient dynamics of a free-base tetraphenylporphyrin (H2TPP) surface-mounted metal organic framework (SURMOF) is spectroscopically characterized and compared with that of H2TPP in ethanol solution. A dramatic increase of the quantum yield of the Soret band fluorescence (S-2 -> S-0) is observed in the H2TPP-SURMOF, which is accompanied by an increase of the S-2 fluorescence lifetime and a broadening of the fluorescence spectra. In contrast, the Q band (S-1) fluorescence is strongly quenched in the H2TPP SURMOF compared with the fluorescence of H(2)TPPin ethanol solution. The observed transient absorption kinetics supports the fluorescence data. The enhanced fluorescence in the SURMOF compared with H2TPP in solution is attributed to the combination of two factors: the alignment of the vibrational energy levels of the dominant Franck-Condon active mode of the Soret and Q bands and the weaker coupling of these modes to the environment.
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| 2. |
- Li, Xiaoxin, et al.
(författare)
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Ultrafast Relaxation Dynamics in Zinc Tetraphenylporphyrin Surface-Mounted Metal Organic Framework
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 122:1, s. 50-61
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Tidskriftsartikel (refereegranskat)abstract
- Ordered porphyrin-based metal organic frameworks (MOFs) may serve as a model for mimicking the natural photosynthesis with highly ordered chlorophylls, i.e., porphyrin-like chromophores. Study of light harvesting and energy transfer as the primary event of photosynthesis is of great importance leading to improvement of photovoltaics overall performance. Detailed characterization of ultrafast dynamics of zinc tetraphenylporphyrin (ZnTPP) surface mounted metal organic framework (SURMOF) is reported by using various steady-state and time-resolved laser spectroscopic techniques, i.e., time correlated single photon counting, fluorescence up-conversion and transient absorption pump-probe with 20 fs resolution. Obtained results in these nanoporous materials were compared with corresponding results for ZnTPP in ethanol measured under the same conditions. Dramatic quenching of both upper excited singlet state S-2 and first excited state SI was observed. Subpicosecond and picosecond lifetimes were detected in transient fluorescence and absorption. Analytical formulas are derived for the linear absorption, steady-state fluorescence, and fluorescence up-conversion signals. Theoretical description excellently reproduces experimental time and frequency resolved signals. Strong quenching of the femtosecond transients in SURMOF is explained in terms of highly efficient Forster resonance energy transfer between the neighboring porphyrin moieties which is caused by a strong spectral overlap of absorption and steady-state fluorescence spectra and quantum coherent energy transfer and redistribution.
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| 3. |
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| 4. |
- Zhou, Yichen, et al.
(författare)
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Upper Excited State Photophysics of Malachite Green in Solution and Films
- 2020
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Ingår i: Journal of Physical Chemistry B. - : AMER CHEMICAL SOC. - 1520-6106 .- 1520-5207. ; 124:21, s. 4293-4302
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Tidskriftsartikel (refereegranskat)abstract
- Relaxation pathways of upper excited electronic states of malachite green (MG) in ethanol and in films are studied by steadystate and time-resolved spectroscopic techniques. In contrast to ethanol, where MG emits weak short-lived spectrally well separated S-2 and S-1 fluorescence with the lifetimes similar to 0.3 and similar to 0.9 ps, MG films show a much stronger broadband fluorescence within 430-700 nm, revealing multiexponential kinetics with the characteristic decay times tau(1) approximate to 1 ps, tau(2) approximate to 10 ps, tau(3) approximate to 0.05-0.8 ns, and tau(4) approximate to 2-3 ns. By the analysis of spectroscopic responses of MG in ethanol and in films as well as by theoretical modeling, we demonstrate that significant increase of fluorescence lifetimes and substantial enhancement of fluorescence intensity in MG films are stipulated by the decrease of efficiency of the S-2 -> S-1 and S-1 -> S-0 internal conversion, which in turn is caused by hindrance of rotation of MG's phenyl rings controlling the S-2/S-1 and S-1/S-0 conical intersections. These findings indicate that MG films may become promising non-Kasha materials (with reasonable S-2 emission) with numerous photophysical and photochemical applications.
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