W.P. Cofino

Highly-resolved fluorescence spectrometry of pyrene on a thin-layer chromatographic plate

Abstract Site-selection spectroscopy, by using suitable laser line excitation, gives epectra of molecules on thin-layer chromatographic plates comparable in quality to Shpolskii spectra. Pyrene is investigated as a model compound.

Quantitative Determination of Polycyclic Aromatic Hydrocarbons in Harbour Sediment via High-Resolution Shpol'skii Spectroscopy

Abstract Polycyclic aromatic hydrocarbons (PAHs) in harbour sediment have been determined by means of Shpolskii fluorometry. Fundamental aspects of this cryogenic high resolution technique are discussed. It provides characteristic spectra of aromatic molecules that can be successfully employed for identification purposes. Extra selectivity is obtained by making use of selective excitation, even with a broad-banded light source. Highly specific quantitative determinations can be achieved, due to the quasi-linear character of the spectra. Deuterated PAHs are suitable as internal standards. Calibration curves with linearity from 10−5-10−6 M down to the detection limit are found, yielding a dynamic range from 2 to 4 decades for the compounds investigated. The reproducibility of the quantitative experiment lies between 6 and 20 per cent. The results obtained with Shpolskii spectroscopy are in good agreement with data found by a standard method of analysis employing fluorescence detected HPLC.

Spectroscopic investigations of photolysis products of organic compounds in Shpolskii matrices. Application to acenaphthene and monomethylnaphthalenes

Abstract It is shown that Shpolskii matrices can be very suitable to acquire quasilinear spectra of trapped unstable species. Photolysis of acenaphthene and monomethylnaphthalenes in Shpolskii matrices yields photoproducts exhibiting highly resolved spectra. It is proposed that in addition to the acenaphthenyl radical the 1-acenaphthenium cation is formed, whereas photolysis of monomethylnaphthalenes produces the methylnaphthyl radicals, the methylnaphthenium cations and the benzocycloheptenium cation.

Site-selection polarization measurements on tetracene in stretched polyethylene films

Abstract The polarization of individual vibronic bands in fluorescence spectra can be established with site-selection experiments using stretched polymer films. This is illustrated with an investigation on the 19000–20000 cm −1 region of the fluorescence of tetracene. The merits and possible applications of the method are discussed.

Jahn-Teller effect in highly resolved optical spectra of the phenalenyl radical

Highly resolved emission and excitation spectra of phenalenyl are reported. Our semiempirical calculations predict E″ symmetry for the lowest excited state. Indeed, Jahn-Teller effects are observed. Force field calculations have been performed to determine the symmetries of vibrations visible in the spectra. The Jahn-Teller coupling is analysed with a scheme of Sloane and Silbey.

Orientation and phosphorescence polarization of planar hetero-aromatic molecules in stretched polyethylene films

Abstract The general applicability of the stretched film technique has been studied from luminescence polarization data of the related homo- and hetero-aromatic compounds (a) benzene and pyrazine and (b) fluorene, carbazole and dibenzofuran. It is shown that corresponding molecules are oriented similarly in stretched polyethylene films. The phosphorescence polarization data of the compounds quinoxaline, carbazole, naphthalene and fluorence are compared and interpreted qualitatively on the basis of spin—orbit and vibronic coupling.

Highly resolved optical spectra of o-durylene

Abstract Highly resolved emission and excitation spectra of o -durylene in n -hexane at 5 K are reported. A tentative vibrational analysis is given. Two modes show an absorption-emission asymmetry which is ascribed to vibronic coupling. The observation of vibronic coupling effects implies that the S 1 state is doubly excited in origin.

Quantitative models to interpret optical polarization data of planar aromatic hydrocarbons in stretched polymer films and application to photoselection spectroscopy

Abstract Quantitative models are presented to interpret polarization data of planar aromatic hydrocarbons oriented in stretched polymer films. Graphs are given of the derived equations and applications are briefly described. The relation between these formulae and those commonly used in photoselection spectroscopy for some specific distributions is discussed. Our expressions permit insight into the observed phenomenon that the theoretical limits of the fluorescence polarization degree in the photoselection technique are rarely attained.

Highly resolved optical spectra of a 2,3-naphthoquinodimethane derivative in a Shpol'skii matrix

Abstract The Shpolskii method yields quasilinear spectra of exo-naphtho [b:3,4] tricyclo [4.2.1.0.2,5] nonane 5 in n-hexane at 5 K. This result is discussed with reference to the “key and hole” rule. Highly resolved spectra of the 2,3-naphthoquinodimethane derivative 4 are obtained by photolysis of 5. The results are comparable with those of o-durylene 3.

Vibronic coupling effects in the highly resolved optical spectra of 1,3-perinaphthadiyl, a molecule with a triplet ground state

Abstract Quasilinear spectra of 1,3-perinaphthadiyl have been obtained in n -pentane and n -hexane by photolysis of cyclopropanoacenaphthylene. The spectra of the biradical display a large absorption-emission asymmetry, which is discussed in terms of vibronic coupling. Our analysis indicates that the two lowest excited electronic states are separated by less than 250cm −1 . The results of open shell PPP and CNDO/S calculations with various CI bases are given and compared with experimental data.