Chmouel R. Goldschmidt

Triplet state formation in the quenching of fluorescence by molecular oxygen

Abstract A pulsed nitrogen laser is applied for studying the quenching of aromatic hydrocarbons fluorescence by oxygen. In non-polar solvents the process induces intersystem crossing to the triplet state with a quantum yield of unity. Effects of solvent polarity suggest that the interaction between S 1 and O 2 ( 3 Σ g − ), leading to T 1 , is charge-transfer in nature.

A new method for absolute absorption cross-section measurements: rhodamine-6G excited singlet-singlet absorption spectrum

Abstract A novel method is suggested to measure the absolute excited single-singlet absorption spectrum of rhodamine by bleaching completely the solution. The molar decadic extinction coefficient of the excited state (ϵ = 4.8 × 10 4 liter mole −1 cm −1 at 440 nm) is estimated directly from the plateau-like absorption signal at very high excitation intensities.

Absorption Spectra of Exciplexes

Absorption spectra of the exciplexes of pyrene, anthracene, biphenyl, and naphthalene with diethylaniline (DEA) as a common electron donor are recorded by applying pulse laser photolysis. The numerous bands appearing in the spectra are analyzed and attributed to transitions from the emitting charge‐transfer state, (A−D+), to higher excited charge‐transfer states [(A−*D+) and (A−D+*)], as well as to locally excited states [(A*D) and (AD*)]. The results indicate that exciplex absorption spectroscopy may provide a new route to the experimental observation of excited molecular states (of D or A), which are not detectable in the ground state spectra of the corresponding molecules.

Fast formation of the hydrated electron by dissociation of excited β-naphtholate

Abstract Excitation to the lowest singlet state of β-naphtholate ion in aqueous solution, (by the absorption of the 3371 A light from a 7 nsec pulse of an N2 laser) is followed within ⩽ 1 nsec by formation of a hydrated electron, e−aq. This process procedes the formation of the fluorescent exoited state and competes with it. Increased temperature increases e−aq formation and decreases fluorescence.

Lasing in some aromatic couples by means of energy transfer

Abstract Low threshold lasing of perylene and 9,10-diphenylanthracene has been achieved by means of energy transfer in binary solute solutions pumped by a nitrogen laser. The low absorption of these compounds to the 3371. A excitation radiation has been overcome by the mechanism of nonradiative dipole—dipole energy transfer. In addition, when a donor has a high molar extinction coefficient at 3371 A and good spectral overlap characteristics with an acceptor, it can serve as an efficient donor for lasing even though it has a low fluorescence quantum yield.

Excited singlet-singlet spectra of anthracene, N,N-diethylaniline and their CT complex

Abstract A transient absorption is observed in anthracene (A)-N,N-diethylaniline (D) solutions in toluene excited by the 3371A line of a nitrogen laser. The lifetime of the transient matches that of the fluorescence of the excited (D·A) charge transfer complex. The absorption is assigned to a transition from the fluorescent CT state to a higher CT singlet of the complex. Excited singlet-singlet absorptions are also observed for the free anthracene and N,N-diethylaniline molecules.

Theoretical approach to laser trabeculotomy

Theoretical aspects of laser characteristics as well as the physics parameters involved in laser trabeculotomy in open-angle glaucoma are put forward. Outflow hydrodynamics and perforation mechanism as well as the required optical matching system are evaluated in detail.

An intermolecular interaction of excited states in crystals and liquids

Abstract Experimental evidence is presented on an excimer-excimer interaction in pyrene crystals and solutions containing a high concentration of pyrene. This interaction is used to explain in part why scintillation pulse shapes when excited by α-particles contain less of an excimer component than when excited by β-particles.

Fluorescence quenching by oxygen as derived from high excitation intensity experiments

Abstract The quenching by oxygen of the fluorescence of concentrated pyrene solutions in toluene occurs in less than 2 × 10 −10 sec. The molecule of O 2 is available for further quenching after this time. The results are interpreted in terms of a mechanism in which a pyrene excimer is quenched by rapid reversible charge transfer complex formation with O 2 followed by energy transfer to the ground state configuation thus formed.

Photoionization of fluorescein via excited triplet and singlet states

Abstract The two-photon ionization of sodium fluorescein in neutral aqueous solution is investigated using laser spectroscopy. Two different pathways are substantiated independently. One proceeds via the first excited singlet state and the subsequent absorption of a photon of UV light (3.8 eV); the other involves the lowest excited triplet state which is ionized by the absorption of a low energy photon of visible light (2.5 eV). For this second pathway the ejection yield, i.e. the probability that the electron definitely escapes from the parent ion pair and solvates, is estimated to be 0.4.