Molecular Spectroscopy of the Triplet State through Optical Detection of Zero-Field Magnetic Resonance

Kinoshita, Minoru; Iwasaki, Noriko; Nishi, N.

doi:10.1080/05704928108060401

Cited by 55 publications

(11 citation statements)

References 76 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The histogram seems to be roughly biexponential which is consistent with the fact that planar aromatic hydrocarbons typically have two short-lived triplet sublevels with similar lifetimes and one long-lived triplet sublevel [9]. Note that the shape of the histogram should change when a short-lived level is coupled to the long-lived level by way of microwaves.…”

supporting

confidence: 67%

Detecting Magnetic Resonance through Quantum Jumps of Single Molecules

1998

View full text Add to dashboard Cite

The fluorescence of a single molecule exhibits light and dark periods which reveal the jumping back and forth between the singlet and triplet manifold. In this paper we demonstrate how microwaveinduced changes to the distribution of the triplet-residence times can be used to detect magneticresonance transitions between triplet sublevels and to determine their kinetics. By synchronizing resonant microwave pulses with the quantum jumps of a terrylene molecule it proved possible to record transient-nutation signals with a high contrast. [S0031-9007(98)05942-0] PACS numbers: 39.30. + w, 33.20.Bx, 76.70.Hb In recent years, optical spectroscopy of single molecules has allowed a wide range of experiments on an increasing number of molecular systems [1]. Still, magnetic-resonance experiments involving a paramagnetic state were as yet demonstrated only for single pentacene molecules [2,3] and individual N-V centers in diamond [4]. Since the signal detected in single-molecule experiments usually consists of the fluorescence emitted by the molecule upon laser excitation, systems apt for single-molecule spectroscopy should have a high fluorescence rate. The fluorescence concerns a transition between the singlet ground state ͑S 0 ͒ and the lowest excited singlet state ͑S 1 ͒. The lowest triplet state T 1 (where two unpaired electrons combine to form a spin S 1) lies below S 1 and becomes occupied, with a low degree of probability, from the S 1 state through a spin-forbidden process called intersystem crossing (ISC). The T 1 state is relatively long lived. While present in T 1 , the molecule does not participate in excitation/emission cycles and thus ceases to fluoresce. For this reason molecules with a low ISC, which visit the triplet state infrequently, are favored in single-molecule spectroscopy. However, this very property makes it hard to perform optically detected magnetic-resonance (ODMR) spectroscopy on the triplet state of a single molecule. In such an ODMR experiment the resonant absorption of microwaves connecting two triplet sublevels is detected through a change of the fluorescence rate. The fluorescence rate may change when two triplet sublevels with different lifetimes are coupled, causing a change in the average triplet lifetime.Instead of detecting the average fluorescence, our method involves the detection and analysis of the length of the dark periods that reflect the presence of the molecule in the triplet state. Such an experiment was performed on terrylene embedded at low concentration in a p-terphenyl host crystal (Fig. 1). Terrylene is known to have a quantum yield for ISC from S 1 to T 1 as low as 10 25 [5] and as yet it proved impossible to observe the magnetic-resonance transitions in its T 1 state. We detected single terrylene molecules by cooling a crystal to 1.8 K and spectrally selecting molecules using a single-mode cw dye laser. Molecule 1 was selected at 17286.08 cm 21 , in the red wing of the origin of the X 2 site [5]. Owing to the short fluorescence lifetime of terrylene (3.8 ns [6]) and...

show abstract

supporting

confidence: 67%

Detecting Magnetic Resonance through Quantum Jumps of Single Molecules

1998

View full text Add to dashboard Cite

show abstract

“…The D * value and T 1 lifetime suggest that the T 1 state possesses mainly a 3 ππ * character. As is known comprehensively, T z sublevels are the lowest in energy for 3 ππ * states [27]. Consequently, the order of the T 1 sublevels was determined to be T x > 0 > T y > T z in energy.…”

Section: Epr Spectramentioning

confidence: 99%

Short-lived and Nonphosphorescent Triplet state of Mexoryl SX, a UV-A Sunscreen

et al. 2020

View full text Add to dashboard Cite

Mexoryl SX (terephthalylidene-3,3'-dicamphor-10,10'-disulfonic acid, Ecamsule) is a watersoluble UV-A absorber. The near-IR phosphorescence spectrum of singlet oxygen generated by photosensitization with Mexoryl SX was not observed in air-saturated water. On the other hand, the time-resolved near-IR phosphorescence spectrum was observed in oxygen-saturated phosphate buffer (pH 7.4). The quantum yield of the singlet oxygen generation (Φ Δ ) was determined to be 0.0021 ± 0.0005. The ability of Mexoryl SX as a photosensitizer is quite low.The question arises as to the quite low Φ Δ value. No phosphorescence was detectable from Mexoryl SX in ethanol at 77 K. We elucidated the nature of the lowest excited triplet (T 1 ) state of Mexoryl SX using a time-resolved EPR technique because this technique is powerful for the study of short-lived and non-phosphorescent T 1 molecules. The strong time-resolved EPR signals were observed. This fact shows that a considerable proportion of the lowest excited singlet (S 1 ) state molecules undergoes intersystem crossing (ISC) to the T 1 state and the deactivation process of the T 1 state is mainly radiationless. The observed zero-filed splitting parameters, T 1 lifetime and S 1 → T 1 ISC anisotropy suggest that the T 1 state can be regarded as a 3 nπ * -3 ππ * mixing state in character and the two unpaired electrons in the T 1 state do not localize on (4methylbenzylidene)camphor, a closely related component. Although the shorter T 1 lifetime (47 ns) prevents T 1 state quenching by ground-state oxygen, the 3 nπ * character may contribute something to the low Φ Δ value.

show abstract

“…This is illustrated by a review [41] of what has been achieved during the first decade after these techniques had been introduced. For nonphosphorescent triplet states alternative optical detection schemes have been devised: fluorescence-detected magnetic resonance (FMDR, [42]) and absorption-detected magnetic resonance (ADMR, [43,44]).…”

Section: The Optical Pumping Cycle -Detection Of Epr Transitions Betwmentioning

confidence: 99%

EPR of photo-excited triplet states: A personal account

Waals

2001

Appl. Magn. Reson.

View full text Add to dashboard Cite

A sketch is presented of the path that has led from Zavoisky's pioneering experiments to modern investigations by electron paramagnetic resonance (EPR) of the phosphorescent (S = 1) triplet state of polyatomic molecules or ions. The group-theoretical method first introduced by Wigner in his analysis of the multiplets of atomic spectroscopy, likewise provides a key for understanding the zero-field splitting and selection rules for radiative decay of the phosphorescent triplet state. Examples to illustrate the progress made through EPR experiments are selected from three fields. (i) Conformational instability on excitation. Both the zero-field splitting and the electron spin density distribution provide unique fingerprints of a triplet state's geometry -structural information of a kind that is nonexistent for singlet states! Illustrations are provided by benzene C 6 H6 and fullerene C60 . (ii) The optical pumping cycle. The spin selectivity of singlet-to-triplet intersystem crossing and radiative decay of the individual spin components of the triplet state is discussed. In practice this selectivity is put to advantage by performing EPR on triplet states in zero-field by means of optical detection. In turn, such experiments have led to a detailed insight into the spin-orbit coupling mechanisms responsible for the spin selectivity of the above processes. The high sensitivity attainable with optical detection has recently culminated in EPR experiments on single molecules. (iii) Quantum interference. In a triplet state of low symmetry two of the spin sublevels may decay to the ground state by the emission of photons of a common polarization (i.e., out of plane for an aromatic hydrocarbon). In such a situation quantum interference between the two decay channels can be induced by an appropriate preparation of the excited state. An example is shown where flash-excitation in the singlet manifold followed by rapid intersystem crossing causes the S = 1 spin angular momentum to be created in a spin state which is not an eigenstate of the zero-field splitting tensor. This nonstationary character of the initial triplet state, which reflects the spin-orbit coupling pathway, is observed through the detection of a spontaneous microwave signal following the 25 ps laser flash.

show abstract

Molecular Spectroscopy of the Triplet State through Optical Detection of Zero-Field Magnetic Resonance

Cited by 55 publications

References 76 publications

Detecting Magnetic Resonance through Quantum Jumps of Single Molecules

Detecting Magnetic Resonance through Quantum Jumps of Single Molecules

Short-lived and Nonphosphorescent Triplet state of Mexoryl SX, a UV-A Sunscreen

EPR of photo-excited triplet states: A personal account

Contact Info

Product

Resources

About