Though already the subject of considerable study, the
nature of 7T*«-n transitions in azaaromatics is still not well
As low temperature crystal techniques have not been
widely used to study these transitions, a series of azanaphthalenes
(better suited to crystal studies than azabenzenes), was
investigated plus pyridine and pyridine-4-d, as well..
The singlet-singlet 7T*-<-n (also for 1-; 2-; 1,2-;
1,3-; 1,6-) absorption spectra have been measured and analysed
for eleven azanaphthalenes 1-; 2-; 1, 2-; 1,3-; 1,4-; 1,5-;
1,6-; 1,7-; 1,8-; 1,4,5-; and 1,4,6-) as mixed crystals (hosts
variously: naphthalene, durene, p-xylene, p-dichlorobenzene) ,
and as pure crystals (1,3- and 1,5- only). Also measured were
the absorption spectra of pyridine and pyridine-4-d in benzene,
and the phosphorescence spectra of 1,3- and 1,5-diazanaphthalenes.
Assignments are systematically presented and discussed.
The mixed crystal spectra of quinoxaline (also recently
reported by Clarke, Hochstrasser and Marzzacco, 1969) provided
information that prompted a reconsideration of the vapour spectrum
(the vapour data was largely due to Byrne, 1967). The
investigation has considerably extended our understanding of this
The spectra of quinoline and 1,6-naphthyridine in
naphthalene showed (for the first time) clear évidence of a lowest
A survey of the azanaphthalene data as a whole was used
to draw general conclusions.
The lack of evidence for the presence of close-lying
n,7T* states and the actual symmetry assignments of observed
lowest states are discussed in relation to the predictions of
The Franck-Condon activity of totally symmetric modes
and the Herzberg-Teller activities of non-totally symmetric
modes are both discussed.
The large number of systems studied has provided an
opportunity to observe many effects of host-guest interaction.
The observed polarisation ratios are discussed in relation to
deep trap theory which does not account for many of the
observations. The presence of multiple sites is discussed and
the observations on the development of phonon structure are
collated and obvious trends indicated'. Solvent shifts are