Near-infrared excitation of alkane ultra-violet fluorescence

Chemical Physics, 1981

A new Nd3'-YAG laser configuration has been used to obtain Ruorescence spectra of a large aromatic molecule with about 12 ~j time-resolution. The data presented are both in the form of time-profiles at selected wavelengths and more importantly tluorescence spectra recorded at 6.7 ps intervals around the irradiation event The sample molecule was 3,4,9,10-dibenapyrene in hexane at 300 K. The major result was the observation of two short-lived transients in the region 389-480 nm characterized by rather difiuse spectra. One, which included a strong "hot-band", was cleariy pulselimited and is assigned to the second excited singkt state. The second transient was considerably weaker and survived beyond the irradiation pulse. This had characteristia of a vibrational quasicontinuum in the St state. Out of these evolved the familiar structured spectrum characteristic of thermalised S1 + So fluorescence. In a related experiment, the ultraviolet fluorescence spectrum (230-340 nm) of two-photon-excited higher states of the same molecule was shown to depend on the time-delay between two excitation pulses. K.-J. Choi et al. / Fluorescence spectrum of a large aromatic molecule 423

Optics and Spectroscopy, 2017

Polarized fluorescence decay in NADH molecules in aqueous solution under two-photon excitation by femtosecond laser pulses has been studied. The excitation was carried out by linear and circularly polarized radiation at four wavelengths: 720, 730, 740, and 750 nm. Time-dependent polarized fluorescence signals were recorded as a function of the excitation light polarization and used for determination of a set of molecular parameters, two lifetimes characterizing the molecular excited states, and the rotation correlation time τ rot. The results obtained can be used to create and prove theoretical models describing the intensity and polarization of fluorescence in NADH involved in the regulation of the redox reactions in cells and tissues of living organisms.

Technical Physics Letters, 2019

The decay of polarized fluorescence in coenzyme NADH in aqueous-methanol solution under two-photon excitation by femtosecond laser pulses within the spectral range of 720-780 nm has been studied. Molecular fluorescence parameters: decay times τ 1 and τ 2 , rotational diffusion time τ rot , and pre-exponential factor ratio a 2 /a 1 have been determined from experiment. The results obtained have been compared with those reported recently in NADH in aqueous solution.

JETP Letters, 2010

1. The investigation of intramolecular vibrational energy redistribution (IVR) in molecules is one of the central items in molecular dynamics research . Interest in the investigation of IVR is primarily associ ated with the development of methods of laser initia tion and/or control of targeted photochemical reac tions. The prospect of implementing selective chemi cal processes in a bond (or a group of bonds) by the resonant excitation of a certain vibration in a molecule is of particular interest. One of the most efficient methods of vibrational excitation of molecules is based on the effect of their multiphoton excitation by reso nant infrared laser radiation (IR MPE). When a mol ecule is excited in this process above the dissociation threshold D 0 , it dissociates; i.e., infrared multiphoton dissociation (IR MPD) occurs (IR MPE and MPD were described in more detail in ). IR MPD is characterized by a high intermolecular (including iso topic) selectivity . At the same time, numerous experiments performed with micro and nanosecond laser pulses show that the intramolecular (including mode) selectivity of IR MPE is absent and the subse quent dissociation of molecules is statistical. This behavior is explained by the fact that IVR prevents the selective photochemical processes in the bond [1, 2]. The reason is that the energy accumulated in an indi vidual resonantly excited vibration above a certain threshold value E st (E st is the so called stochastization threshold, see, e.g., ) is redistributed over the other molecular vibrations until achieving equilibrium. This process leads to the loss of mode selectivity of excita tion and, finally, to the statistical character of the sub sequent reactions, in particular, the dissociation of molecules. The E st value for small (five to seven atomic) molecules is 4 to 7 × 10 3 cm -1 . It is also assumed that the characteristic time of IVR lies in the pico and subpicosecond ranges .

The Journal of Physical Chemistry B, 1999

At high laser pulse excitation energies the fluorescence spectrum of all-trans-1,6-diphenyl-1,3,5-hexatriene, DPH, undergoes distortion that can be modeled as the development of a new broad fluorescence, λ max ) 497 nm, which builds up biphotonically with increasing excitation laser pulse power. This phenomenon is observed upon excitation at either 266 or 355 nm in a variety of organic solvents, provided [DPH] and excitation intensity are sufficiently high. Four possible sources for the distortion of the fluorescence spectrum are investigated: (1) excimer emission arising from DPH radical cation/anion pairs, (2) bicimer fluorescence from the encounter of two S 1 states, (3) S n f S 1 fluorescence, and (4) self-absorption due to overlap of the fluorescence with transient absorption spectra. The first three possibilities are ruled out. The fourth is viable, revealing an effective transient absorption spectrum that agrees well with the known S n r S 1 absorption spectrum at long wavelengths.

The journal of physical chemistry letters, 2017

Fluorescence upconversion and transient absorption techniques are used to explain the source of the intense red/near-infrared emission of crystalline 4-dimethylamino-2'-hydroxychalcone. We found that the initially excited enol form undergoes tautomerization in 3 ps to form the keto tautomer. The latter is stable in the ground state as a consequence of J-type aggregation in the crystal packing and is manifested in an absorption peak at 550 nm that spectrally overlaps with the short-lived enol emission, leading to self-reabsorption and adding a factor to the complete depletion of the enol emission. Relaxation of the keto tautomer takes place in the form of intense fluorescence (600-750 nm) with 1.7 ns lifetime. The different spectroscopy in solution is due to vibrational cooling (300 fs), followed by solvation dynamics (5 ps in methanol) and twisting of the hydroxyphenyl ring (16 ps), before relaxation of the enol tautomer in the form of weak green fluorescence with 350 ps lifetime.

Chemical Physics Letters, 1984

The Journal of Physical Chemistry, 1983

To our knowledge, there are no previous results for CO or C02 hydrogenation in well-defined systems with poisons and promoters used at the same time. However, previous studies on Fe catalysts have shown that addition of K increases the resistance of the catalysts to S p~isoning.~'?~~ Our results show that CO formation proceeds in the presence of both K(a) and S(a) as if the S(a) were absent. As noted previously, the effect on CHI production seems to be a coverage-weighted average of the individual effects of S(a) and K(a). This supports the idea that the effects of S(a) and K(a), separately and together, reflect the changes of electron density in the metal rather than any direct, local-site effects, at least for CHI formation. Much more study, however, should be directed into this area to gain a better understanding of these processes.

Applied Spectroscopy, 2003

Quantum Electronics, 2002

The main stages of the development of the photochemical method for exciting near-IR, visible, and UV gas lasers are briefly reviewed on the basis of studies performed at the Department of Quantum Radiophysics at the P.N. Le-bedev Physics Institute and jointly with other institutes within the framework of a program for creating high-power explosion-pumped lasers under the supervision of academician N.G. Basov.