Spectroscopy of o-diazahelicenes of C2v /C2 symmetry

Publication Type

Journal contribution

Authors

Greiner, G.; Rau, H.; Bonneau, R.

Year of publication

1996

Published in

J. Photochem. Photobiol., A

Band/Volume

95/2

Page (from - to)

115-25

The absorption and emission properties of members of the series benzo[c]cinnoline ("diazatrishelicene"), diazapentahelicene and diazadibenzoheptahelicene change in a characteristic way. The solvent properties influence strongly the phosphorescence/fluorescence ratio. For heptahelicene, this ratio shows an intricate dependence on the excitation wavelength, which has not been obsd. previously. A common feature is the very low emission yield. The energies of the excited (n,.vpi.*) and (.vpi.,.vpi.*) states of non-planar pentahelicene and heptahelicene are crucial for these properties; very effective radiationless deactivation of the lowest triplet states, presumably due to a pseudo-Jahn-Teller effect, is obsd. Good agreement is found between the empirical and calcd. sequences in the energy diagram of the excited states.