Knowledge Bank

We have investigated ($4.2\circ -90\circ$K) the absorption and emission spectra of anthracene in naphthalene at low concentration (approximately $106:1$) and in phenanthrene at higher concentrations (approximately $104:1$). The results agree, in general, with published data. However, the bands are better resolved and a more detailed assessment of the lattice participation in the first anthracene singlet transition has been made possible. The participation of optical and acoustic phonons is discussed in some detail. Anthracene in these two hosts does not exhibit the striking dependence of the azulene (naphthalene host) absorption and emission spectra on concentration. (Kazzaz and Zahlan, unpublished). In the azulene case the 0-0 phonon side band's intensity is much greater in concentrated than in very dilute mixed crystals. The distribution of anthracene emission intensity among the $0-0$ and vibronic transitions is different in the phenanthrene and naphthalene hosts. In naphthalene the band system around $0-0+1400cm-1$ comparable in intensity to the 0-0+phonons system; while in phenanthrene this $0-0+1400cm-1$ system is some ten times stronger than the $0-0$ system. The fluorescence intensity distribution is temperature dependent.