Synthesis and photochromic properties of ladderized poly(p-phenylene-alt-9,10-anthrylene)s

We report here the synthesis and characterization of stepladder and ladder poly(p-phenylene-altanthrylene) s (SLPPPA and LPPPA respectively) containing 9,10-anthrylene building groups within the main chain. The polyketone ladder polymer precursors are prepared by palladium-catalyzed Suzuki-type cross-coupling. The solution optical spectra of SLPPPA and LPPPA exhibit broad absorption bands with large Stokes shift unusual for rigid, ladder-type polymers. SLPPPA shows an intense yellow emission with a maximum at 584 nm while LPPPA is more red-shifted in emission with a maximum at 693 nm due to the planarization of the aromatic repeat units. Cyclic voltammetry studies reveal that both SLPPPA and LPPPA undergo fully reversible p- and n-doping processes. The methylene- bridged 1,4-di(10-phenylanthracen-9-yl) benzene LMC and the bis(methylene)bridged 9,10-diphenylanthracene SLMC are also synthesized, they serve as ladder and stepladder model compounds respectively and their optical properties are discussed in comparison with the above polymers. The stepladder derivatives (SLMC and SLPPPA) are found to form endoperoxides in the presence of visible light in a thermally reversible process whereas the ladder derivatives (LMC and LPPPA) undergo irreversible photooxidation.