Phosphorescence spectra of 1,5-naphthyridines

The polarized phosphorescence spectra of 1,5-naphthyridine and its d6 isomer in durene and in durene-d14 mixed crystals have been obtained at 4°K. The lowest singlet state is at 27123 and 27200 cm-1, whereas the corresponding triplet state is at 23215 and 23288 cm 1 for the proto and deutero compounds, respectively. The phosphorescence lifetime in durene crystals is 0.23 sec.140 The polarized spectra (4°K) of 1,5-naphthyridine and its d6 isomer in naphthalene have also been examined. There is a difference between the spectra in naphthalene and in durene attributable to a decrease in the strong vibronic coupling that is considered to exist between the n- n state and the higher n -> n states.141 TheEPR spectrum of 1,6-naphthyridine in its lowest triplet state has been observed for solid solutions in single crystals of durene. The nuclear hyperfine structure allows an estimate of 0.14 to be made for the spin density on the nitrogen atom in the 1-position.142... 

Polarized phosphorescence spectra of 1,5-naphthyridine 1 (1959MI1, 1973MI2, 1981JSP345) and the ESR spectrum of 1,6-naphthyridine 3 (1975MI1) and hexa-hydro-l,8-naphthyridinetetrazole were recorded (1998MI6). 

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