On the optical properties of fluoranthenopyracylene ladder type molecule series

This work reports on theoretical and spectroscopic study of recently prepared thermally and chemically stable ladder type molecules with extended π-conjugation consisting of fluoranthenopyracylene units. Density functional theory (DFT) and time-dependent DFT calculations were performed for the electronic ground and lowest excited states to obtain optimal geometries. Our calculations indicate both a planar structure of the central ladder part and a negligible influence of lateral phenylene rings. Geometrical changes upon the electronic excitations are indicated in the center of the molecular skeleton. Experimental absorption spectra of the investigated series measured in ortho dichlorobenzene consist of several bands, with well-distinguished vibronic structure. Effective conjugation length for excitation and fluorescence energy was estimated to be 10 and 9 repeating units, respectively.