A study has been made of the electronic transitions between the lowest triplet state of anthracene and its ground state. Low-temperature spectroscopic study of the phosphorescence revealed a sharp emission band with a 0,0-frequency (T→S) at 14 927 cm—1 (EPA rigid glass solution at 77°K). A vibrational analysis in terms of known Raman frequencies indicates that the transition is of a u→g allowed type. The T←S absorption band was observed in anthracene with the 0,0-frequency at 14 850 cm—1 (solution at 293°K). The study of the phosphorescence spectra of seven different chlorinated anthracenes confirmed the assignment of the anthracene lowest triplet. This study re-establishes the earlier value obtained by Lewis and Kasha, and rejects the recent value deduced by Reid. A correlation of the above results for anthracene with calculations and observations on related polyacenes indicates that the lowest triplet of benzene is 3B1u (in D6h), and for naphthalene, anthracene, and naphthacene the lowest triplet is 3B2u (in D2h). The perturbing singlets which mix with these triplets are obtained from previously derived rules for spin-orbital coupling in molecules.

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SynopsisIn solvent spinning of polyacrylonitrile from DMF or DMSO, it is observed that complete removal of solvent is rather difficult. It is shown that addition of Lithium salt, e.g., lithium bromide to the solution before casting a film helps in removing the solvent easily. The probable mechanism of the action of lithium salt in solvent removal is investigated, and it has been shown that the formation of coordinate linkage with the ion stops solvent bonding.

synopsisAccurate estimation of amino acids composition has been carried out for hydrolysates of four varieties of Indian silks, viz., Mulberry, Tasar, Eri, and Muga. These studies have revealed that the hydrolysate (hydrofibroin or crystalline region) in the case of Mulberry consists of glycine, alanine, and serine, whereas in the caw of Tasar, Eri, and Muga, it is found to be mainly alanine. Other amino acids were also found to be present in the hydrolysate of these silks. But, the quantities present in each case were found to be negligible when compared to those amino acids cited above. Furthermore, these results are in conformity with the structure elucidation made by infrared spectral studies and x-ray diffraction.

Optical luminescence of amorphous bright poly(ethy1ene terephthalate) (PET) films and the changes in luminescence due to certain morphological changes have been studied at 77K to identify the luminescent centres in this polymer. The emission spectrum consists of both fluorescence and phosphorescence with distinct band peaks at 304, 326, 365 nm corresponding to fluorescence and at 426, 453, 476 nm corresponding to phosphorescence. Comparison of the PET emission spectrum with that one from dimethyl terephthalate microcrystals indicates that the emitter in the polymer is most probably the basic terephthalate unit. Polarized absorption and emission studies in oriented and unoriented PET films also support this observation. Change in the relative intensity distribution on changing the crystallinity of the film suggests that each of the 304, 326 and 365 nm fluorescence bands arises from different environments of the emitting centre. On y-irradiation, a large increase in emission intensity is observed. This is explained on the basis of formation of a radical which in turn causes a large inductive effect on the benzene rings. ZUSAMMENFASSUNG:Optische Lumineszenz amorpher klarer Folien aus Polyathylenterephthalat sowie Lumineszendnderungen aufgrund morphologischer Variation wurden bei 77 K untersucht, um die Lumineszenzzentren zu identifizieren. Das Emissionsspcktrum besteht aus Fluoreszenz und Phosphoreszenz mit definierten Fluoreszenzpeaks bei 304, 326 und 365 nm sowie definierten Phosphoreszenzpeaks bei 426,453 und 476 nm. Ein Vergleich des Polyathylenterephthalat (PET)-Emissionsspektrums mit dem von Dimethylterephthalat-Mikrokristallen zeigt, dal3 die Emission hochstwahrscheinlich von der Terephthalateinheit ausgeht. Polarisationsabsorptions-und -emissionsuntersuchungen an orientierten und unorientierten PET-Folien unterstutzen diese Beobachtung. Anderungen in der Verteilung der relativen Intensitat bei Anderung der Folienkristallinitlt zeigen, daB jede der erwahnten Fluoreszenzbanden durch verschiedene Umgebung des Emissionszentrums 33 M. R. Padhye and P. S. Tamhane verursacht wird. Bei y-Strahleneinwirkung wird eine groL3e Steigerung der Emission beobachtet. Dies wird durch Radikalbildung erklart, die ihrerseits einen grol3en induktiven Effekt auf die Benzolringe ausiibt.