Spectroscopy and Photophysics of Monoazaphenanthrenes I. Absorption and Fluorescence Spectra of Phenanthridine and 7,8-Benzoquinoline

Spectroscopy and Photophysics of Monoazaphenanthrenes III. Luminescence of Phenanthridine and 7,8-benzoquinoline in Crystalline State

“…n-hexane or cyclohexane) at room temperature [9]. Within the error limit, the fluorescence spectrum is independent of the wavelength of excitation.…”

“…There is a shoulder around 28000 cm −1 , and some other shoulders are coming before the maximum located at ∼ 26100 cm −1 . This is somewhat surprising, especially in view of the fact that in n-hexane solution at room temperature, fluorescence spectra of PHN and BQ [9] have a very similar vibrational structure (they differ only in the position of the 0-0 origin transitions by 246 cm −1 ). Even more surprising is the observed temperature behavior of the fluorescence spectrum of BQ, which is illustrated in Fig.…”

“…The results of our recent investigations of absorption and fluorescence spectra of phenanthridine and 7,8-benzoquinoline in non-polar (and non-hydrogen bonding) solvents, such as n-hexane or cyclohexane, and in strongly polar (and hydrogen-bonding) methanol solutions have clearly demonstrated that the first excited, S 1 , singlet state in both molecules is of ππ * character [9]. This conclusion was further confirmed by ab initio analysis of molecular parameters and electronic spectra of both molecules, according to which [10] the lowest excited singlet state of nπ * character is the second, S 2 , and the third, S 3 , excited state within the singlet states manifold of PHN and BQ, respectively.…”

Fluorescence Spectra of Phenanthridine Isolated in the Supersonic Jet Expansion - An Ab Initio Analysis

“…[7]), which as an aromatic molecule does not contain N atom at all. With such observations as above, one arrives at the conclusion that in all three molecules -both monoazaphenanthrenes as well as in their parent aromatic hydrocarbon -an electronic transition in the first excited singlet state is delocalized over entire aromatic rings system in very similar manner (which intuitively is not surprising, in view of the fact that in all three molecules S 1 state is of ππ * character [5,9]). A complete information about the deformation of a given molecule caused by an electronic transition to its excited state, must also contain the changes of the angles between adjacent bonds.…”

“…Hence, in some cases fluorescence and/or phosphorescence of N-heterocyclic aromatic hydrocarbons are extremely sensitive to the solvent. In the case of monoazaderivatives of tricyclic aromatic hydrocarbons (such as anthracene and phenanthrene) solvent-sensitivity of fluorescence seems to be related to the relative energetics of 1 (π, π * ) and 1 (n, π * ) excited singlet states in a particular molecule under consideration, as well as to the capability of non-bonding n-electrons to the formation of the hydrogen bonds [3][4][5].…”