Synthesis of fluorosolvatochromic phenanthrenyl-substituted benzoquinolizinium derivatives

Abstract

The biaryl derivatives 8-(phenanthren-9-yl)benzo[c]quinolizinium and 9-(phenanthren-9-yl)benzo [b]quinolizinium were synthesized by a Suzuki-Miyaura coupling, and their steady-state absorption and emission properties were investigated. Whereas the absorption properties are essentially independent of the solvent properties, these compounds show a pronounced fluorosolvatochromism. Namely, they exhibit their lowestenergy maximum in aprotic, polar solvents and significantly blue-shifted emission bands in polar protic solvents. Notably, comparison of three different phenanthrenyl-substituted quinolizinium derivatives revealed that these fluorosolvatochromic properties are essentially independent of the annelation pattern of the quinolizinium unit, given that the aryl substituent has the propensity to form a sufficiently stabilized radical cation upon a photoinduced charge shift in the biaryl derivative.