G. Nouchi

Twisted internal charge transfer fluorescence of para-N,N-dimethylaminobenzonitrile in rigid matrix at room temperature

Abstract The dual fluorescence of para-N,N-dimethylaminobenzonitrile is observed for the first time in a rigid matrix at room temperature (polyvinylalcohol). A relationship between the twisted internal charge transfer (TICT) fluorescence and the formation of a ground-state hydrogen bonded complex is shown.

Tict fluorescence in rigid matrices: α-delayed fluorescence

Abstract The observation of the dual fluorescence of 4-N,N-dimethylaminobenzonitrile (DMABN) in polyvinylalcohol has been extended to other matrices able to act as hydrogen-bond donors (nylon and polyurethane) and to related molecules. A model of α-delayed fluorescence is proposed to account for the properties of the luminescence in rigid matrices. This proposal is consistent with: the positive polarization of the anomalous fluorescence (room temperature) while the polarization of phosphorescence is negative (at 77 K); the quenching of the anomalous fluorescence by lowering the temperature; the very long lifetime (τ ≈ 1 s) of the anomalous fluorescence, in the same range as the phosphorescence lifetime.

Dynamics of the reactions of aluminium atoms studied with pulsed crossed supersonic molecular beams

The reactive collisions of aluminium atoms with O2, CO2 and SO2 have been studied with crossed pulsed supersonic molecular beams. Aluminium atoms were obtained from vaporization of an aluminium rod, using an excimer laser. They were probed, together with the product AlO, by laser-induced fluorescence. Collision energy ranges were 0.08–0.49 eV for Al + O2, 0.14–0.53 eV for Al + CO2 and 0.30–1.19 eV for Al + SO2. The variation of AlO rovibrational distributions and reactive cross-sections with collision energy has been determined for each reaction. The value D0°(AlO)= 5.26 ± 0.03 eV has been found for the AlO dissociation energy.

Dual Fluorescence of 4-N,n-Dimethylaminopyridine - Role of Hydrogen-Bonded Complex in the Ground-State

Abstract A correlation is shown between the appearance of the dual fluorescence of 4- N,N -dimethylaminopyridine (DMAP) solutions and the formation of hydrogen-bonded of complexes in the ground state. A comparative absorption study between pyridine, N,N -dimethylaniline and DMAP shows that the hydrogen-bonded complex is situated on the amino nitrogen of DMAP. A “pretwisted” conformation of DMAP in the ground state isassumed due to this hydrogen-bonded complex. Simulations by intermolecular interaction calculations and spectroscopic calculations (CNDO/s) confrim the “twisting” influence of water molecules (and/or any other hydrogen bonding) on the amine in the ground state. This “pretwisting” in the ground state by hydrogen bonding is common in many other aromatic amines. Moreover, the deforming role of hydrogen bonding in the ground state seems to be a general phenomenon in flexible aromatic molecules.

Reactive scattering using pulsed crossed supersonic molecular beams. Example of the C+NO→CN+O and C+N2O→CN+NO reactions

The dynamics of the C+NO→CN+O and C+N2O→CN+NO reactions are reinvestigated using a pulsed supersonic crossed molecular beam apparatus. Laser vaporization of graphite at the exit of a pulsed nozzle is used to produce the atomic carbon beam. Laser induced fluorescence spectra of the CN scattered product have been obtained for both reactions.

Specific hydrogen bonding interaction versus the “free volume” model for TICT molecules in polymeric matrices

Abstract The absence of TICT emission in non-hydrogen-bonded polymers is confirmed. In such polymers the abnormal fluorescence F a appears when water traces are introduced at the same time as the solute. Contrary to the recent results of Al-Hassan and Azumi a very intense TICT fluorescence (long-lived) is observed for p -dimethylaminobenzonitrile (DMABN) in polyvinylalcohol (PVA). We explain this discrepancy by the quenching of the TICT fluorescence by acetic acid contained as an impurity in their PVA. The quasi-independence of the emission on molecular weight for the same kind of polymer, and the significant decrease of F a by softening the matrix, rule out the “free volume” model as being solely responsible for the TICT emission in polymeric matrices. The specific solute solvent interaction has to be retained.

Auto-association of tetracene in solution

Abstract A systematic study of the absorption and fluorescence spectra of solution of tetracene led us to the discovery of two auto-associated species: microcrystals, improperly called a dimer by several authors and another species, which could be the true dimer.

Experimental investigation on the electronic properties of 2,2′-biquinoline. A study by UV-visible spectroscopy

Abstract A large number of works have been done on double molecules. For 2,2′-Biquinoline (2,2′-BQ) (Fig-1), the studies were investigated essentially for the triplet state by various techniques; steady state ESR[1], raman and ODMR techniques [2]. Some works on the 2,2′-BQ complexes have stressed the close connection between the metal complex formation and the conformation change of the ligand molecule [1,3,4]. Our interest in this molecule arises from our earlier observations on other double molecules such as 1,1′-binaphthyl and 2,2′- binaphthyl [5,6] and 9,9′-bianthryl [7,8]. In the present work, the investigation was carried out experimentally on 2,2′-BQ for which original results are given.

Room-temperature phosphorescence of 2,2′-biquinoline in polymeric matrices

An original and very strong long-lived emission of 2,2′-biquinoline is observed in hydrogen-bonded polymeric matrices only. This long-lived emission (Τd = 1 s) is ascribed to room-temperature phosphorescence (RTP) because of the large value of the decay time, the temperature-dependence, and the polarization results.The existence of hydrogen-bonded complexes in the ground state is assumed to be the origin of the RTP. They involve changes in the conformation of the 2,2′-biquinoline.

A striking observation on the fluorescence of a twisted intramolecular charge transfer (TICT) molecule used to probe polymer dynamics in the bulk state

An anomalous effect on the twisted intramolecular charge transfer (TICT) phenomenon of 4-(N,N-dimethylamino) benzonitrile (DMABN) dissolved in elastomers such as poly(propylene oxide), poly(ethylene oxide) has been observed. Under irradiation, the normal fluorescence of DMABN in these matrices has been found to increase strongly while the emission arising from the TICT state decreases slightly.