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Journal ArticleDOI

Investigation of the lowest triplet state of free base porphin by microwave induced changes in its fluorescence

15 Aug 1973-Chemical Physics Letters (North-Holland)-Vol. 21, Iss: 2, pp 221-225
TL;DR: The zero-field splitting of the non-phosphorescent lowest triplet state of free base porphin is measured by observing microwave induced changes in the fluorescence of this molecule as a guest in a Shpolskii-matrix of n -octane at 4.2°K.
About: This article is published in Chemical Physics Letters.The article was published on 1973-08-15. It has received 88 citations till now. The article focuses on the topics: Porphin & Triplet state.
Citations
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Journal ArticleDOI
01 May 1993-Nature
TL;DR: In this paper, the triplet state of a single pentacene molecule embedded in a p-terphenyl host crystal was observed for a single molecule in a single-molecule environment.
Abstract: THE introduction of optical detection methods for observing magnetic resonance transitions in metastable paramagnetic states1–4 has contributed enormously to our understanding of the properties of photoexcited molecules in condensed phases. In such experiments the luminescence intensity is recorded as a function of the frequency of an applied microwave field. At resonance with transitions between sublevels of a metastable paramagnetic state, the lifetime of the metastable state is altered and a consequent change in the luminescence intensity is observed. Here we report the observation of such optically detected magnetic resonance transitions for the triplet state of a single pentacene molecule embedded in a p-terphenyl host crystal. This result has been obtained by combining the conventional optical detection technique for observing magnetic resonance transitions1–4 with the new single-molecule optical detection methods developed recently5,6. This observation opens the way for magnetic resonance studies in condensed phases with single-molecule sensitivity.

233 citations

Journal ArticleDOI
TL;DR: In this paper, the photoisomerism following selective excitation with a dye laser into the S 1←S 0 transition of either of the two forms, for H2P and D2P (two inner hydrogens replaced by deuterium), was investigated.
Abstract: It is known that the porphyrin free base (H2P) can be incorporated in an n-octane Shpol'skii matrix. In slowly grown crystals the solute molecules occur in two orientations, which are co-planar and have their N-H … H-N axes at right angles; in the S 1↔S 0 ‘quasi-line’ absorption and fluorescence spectra they can be distinguished by a relative shift of 65 cm-1 of their spectral features. By irradiation with light the two species are transformed into one another via a shift of the two inner protons. Here a study is presented of the photoisomerism following selective excitation with a dye laser into the 0-0 band of the S 1←S 0 transition of either of the two forms, for H2P and D2P (two inner hydrogens replaced by deuterium). At 4·2 K the reaction proceeds in both directions; for H2P the reaction in one direction appears to be 10 per cent faster than in the other, for D2P the absolute rates are nearly ten times lower than for H2P and not measurably different in the two directions. The reactions are not signif...

180 citations

Journal ArticleDOI
TL;DR: In this paper, the wavelength for heavy atom enhanced phosphorescence was unambiguously established by time resolved excitation spectra in 50% EPA and 50% ethyl iodide at 77 K for protoporphyrin (795 nm), mesoporphrin (773 nm), octaethylporphin (768 nm), and porphin (785 nm).

150 citations

Journal ArticleDOI
TL;DR: This review has tried to emphasize work on the triplet state of chlorophyll in photosynthetic and related systems which has appeared since previous reviews were published, and to demonstrate the impact that the newly available crystal structure has had on many of these studies.

132 citations

References
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Journal ArticleDOI
TL;DR: In this article, three pairs of microwave transitions with widths of a few MHz are found, all of them corresponding to a decrease in phosphorescence intensity, corresponding to the Shpolskii effect, and it was further established that by pumping either of these transitions a third one can be detected at the difference frequency, so that the order of the levels must be X>Y>Z (or reverse)
Abstract: Phosphorescence microwave double resonance experiments are reported on Zn porphin at 1·2 K In glassy solution very broad resonance transitions are observed However, for Zn porphin in a crystalline n-octane matrix—a system known for its sharp optical spectra (Shpolskii effect)—three pairs of microwave transitions with widths of a few MHz are found, all of them corresponding to a decrease in phosphorescence intensity By studying the behaviour of the signals for various methods of preparation of the sample and as a function of the optical bandwidth of excitation and detection, one pair of transitions could be assigned to monomeric solute molecules The corresponding zero-field splittings are |X - Z| = 1355, |Y - Z| = 806 MHz It was further established that by ‘pumping’ either of these transitions a third one can be detected at the difference frequency, so that the order of the levels must be X> Y>Z (or reverse) The results indicate that the molecule no longer possesses a four-fold axis in the excited st

101 citations

Journal ArticleDOI
TL;DR: In this paper, the absorption and fluorescence spectra of Zn porphin in an n-octane single crystal at 4·2 K are reported in the region between 17 400 and 18 500 cm-1.
Abstract: The absorption and fluorescence spectra of Zn porphin in an n-octane single crystal at 4·2 K are reported in the region between 17 400 and 18 500 cm-1. A strong peak appears in both spectra at 17 961 cm-1 and is assigned to the origin of one component (|x, 0>) of the nearly degenerate Q-band. In absorption a second strong line occurs at a frequency δ = 109 cm-1 above the first; a corresponding line is almost totally absent in the emission spectrum at 4·2 K, but it appears as a hot band of appreciable intensity when the temperature is raised to 80 K. This feature is assigned to the origin of the other component (|y, 0>) of the Q-band. The lifting of the degeneracy of the Q-band is interpreted as a crystal field splitting of the Jahn-Teller unstable 1 Eu state. The Zeeman effect is investigated for the 0–0 transition of the phosphorescence spectrum and the |x, 0> and |y, 0> components of the Q-band absorption spectrum. From the phosphorescence experiment it is concluded that the great majority of the ZnP gu...

64 citations

Journal ArticleDOI
TL;DR: The theory and observation of microwave induced population inversion within triplet magnetic sublevels in zero field is presented in this paper, where inversion via adiabatic fast passage can be measured quantitatively by changes in triplet phosphorescence and can be accomplished easily and with microwave field strengths even lower than are required for cw saturation.
Abstract: The theory and observation of microwave induced population inversion within triplet magnetic sublevels in zero field are presented. It is shown that inversion via adiabatic fast passage can be measured quantitatively by changes in triplet phosphorescence and that population inversion can be accomplished easily and with microwave field strengths even lower than are required for cw saturation. Parameters affecting the ability to invert the sublevel populations, such as dipolar interactions, microwave power, and sweep rates, are studied. General equations relating the intensity of phosphorescence and the fraction of inversion to parameters associated with energy transfer processes into and from the triplet state such as intersystem crossing and radiative and radiationless relaxation are derived and measured for the 3π π* state of 2,3‐dichloroquinoxaline.

22 citations