Synthesis and Photophysical Properties of Benzo[c]phenanthrene Derivatives

Three polycyclic aromatic hydrocarbons derived from benzo[c]phenanthrene have been synthesized through a one-step procedure involving palladium Suzuki coupling and are characterized by ¹H and ¹³C NMR, MS and HRMS spectroscopies. UV-vis absorption and fluorescence properties of these π-conjugated compounds have been evaluated in solutions and strong emission in the blue region of the visible spectrum was noted. The optical spectra of these small polycyclic aromatic compounds are unusual since absorption is entirely in the UV region (λmax = 281-285 nm), yet fluorescence occurs at 410-422 nm. This equates to a Stokes shift of 1.32-1.39 eV (10756- 11256 cm⁻¹) and is among the large Stokes shifts that have been reported for small molecules, making them promising candidates for optoelectronic applications.