C. Cazeau-Dubroca

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.

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.

Photophysical study of benzimidazolone and its derivative molecules in solution

The absorption and fluorescence spectra of benzimidazolone (compound I) and three of its derivatives: CH3-benzimidazolone (compound II), Cl-benzimidazolone (compound III) and N,N-dimethylbenzimidazolone (compound IV) have been registered in 3everal solvents. One band is observed in all the considered spectra. The weak red shifted band detected when the solvent polarity increases is mostly due to dipolar interaction between solute and solvent molecules. Furthermore, approximate dipole moment values for the excited state have been estimated using Stokes-shifted data and ab-initio calculations on the ground state. Fluorescence quantum yields and fluorescence lifetimes have been evaluated for each compound in ethanol as the solvent. The effect of substitutions on the spectroscopic properties of these molecules has been found to be more important in the case of compound III.

Complexation versus aggregation of indoles in glassy hydrocarbons

Abstract It is shown, on the basis of recent data on the aggregation phenomenon and of spectroscopic considerations, that alterations of the indole absorption and fluorescence spectra in glassy hydrocarbons at low temperatures and low concentrations are not due to a previously alleged aggregation. It is an impurity, probably water, which causes the solute complexation. This phenomenon can occur with many proton-donor solutes that are able to form a hydrogen bond with the impurity.

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.

Simulation théorique du spectre d'absorption UV du carbazole et de quelques molécules analogues: Theoretical simulation of UV absorption spectrum of carbazole and some homocyclic analogues

The UV absorption spectra structures of carbazole, fluorene and dibenzofurane are studied using the atom monopole-dipole interaction (AMDI) model and atomic dipolar polarisabilities and effective charge given by Fraga. The absorption spectra corresponding to these molecules and their self-associations are presented. The original obtained results are discussed and compared to previous works.

Multiple fluorescences anomaly of 9,9′-bianthryl in solutions

Abstract UV–VIS fluorescence and excitation spectra of 9,9′-bianthryl (BA) in methylcyclohexane (MCH), n-butylchloride (NBC) and acetonitrile (CH3CN) were measured at room and liquid nitrogen temperatures. Three fluorescence bands have been observed depending on the solvent polarity and temperature. In addition, approximate excited state dipole moments have been calculated, and found such as: μe=0 D (debye) (in NBC at 77 K ), 11≤μe≤14.43 D (in all solvents at room temperature and in CH3CN at 77 K), and μe≈19.70 D (in CH3CN at room temperature). On the basis of these results, a ‘multiple states’ model has been suggested. So, the fluorescences observed can originate either from: (i) a locally excited state (LE) with no charge transfer and with a twist angle of 90°, around the C9–C9′ bond; (ii) a partial intramolecular charge transfer (PICT) state with an intermediate twist angle; (iii) a twisted internal charge transfer state (TICT) with a full charge transfer and with a twist angle of 90°.

Structural and energy properties study using the AM1 calculations of aza-azulenes in their ground state

Abstract AM1 calculations with complete optimization have been carried out on the azulene molecule and its derivatives such as 1-aza-azulene and 1,3-diaza-azulene. We show that AM1 is an appropriate method for predicting the structure and energy properties of azulene. Experimental values are found with good accuracy and computer results are analogous to those obtained by sophisticated methods such as the ab initio method (6-31G ∗ ). We describe a complete theoretical study of the structural and energy properties of 1-aza-azulene and 1,3-diaza-azulene in their ground states using the same method with full geometry optimization. From the theoretical finding, the most stable conformations are proposed. Otherwise, these geometrical conformations are preserved in order to determine some spectroscopic values of these compounds using the CNDO/M method. Our results are in qualitative agreement with the experimental data.

Experimental evaluation of (LE) and (TICT) states dipole moments of 9,9′-Bianthryl, 10-Bromo-9,9′-Bianthryl and 10-Cyano-9,9′-Bianthryl

Abstract A comparative study on the solvation induced intramolecular charge transfer in the excited state has been made for 9,9′-Bianthryl (BA), 10-Bromo-9,9′-Bianthryl (BABr) and 10-Cyano-9,9′-Bianthryl (BACN) by fluorescence measurement at room temperature. The study of this fluorescence in liquid solutions shows a strong dependence of Stokes shift versus the dipole moment of the solvents. Experimental results show an important dipole moment variation between ground and TICT (Twisted Intramolecular Charge Transfer) states, whereas this variation between ground and LE (locally excited) states is very weak, when the hydrogen atom in position 10 of (BA) is substituted by a bromine or cyano group respectively.