Arene-functionalized polyisocyanides: photophysics of well-defined homopolymers and block copolymers for efficient light harvesting

Steady-state and time-resolved fluorescence spectroscopy of the homopolymers and di- and triblock copolymers of 2-naphthylethylisocyanide (7), 9-anthrylethylisocyanide (10), and 2-phenanthrylethylisocyanide (11) exhibit emission from the isolated chromophores, i.e., naphthyl, anthryl, or phenanthryl, upon excitation at 284 or 354 nm. The absence of excimer emission in the fluorescence spectra of all these homopolymers is indicative of a rigid polymeric backbone. Fluorescence quenching in diblock copolymers containing a dimethylaniline donor block and a naphthalene or anthracene acceptor block takes place through directional energy migration to the acceptor–quencher interface. The migrating excited state is then quenched at the interface either by photoinduced electron transfer in the anthracene–dimethylaniline diblock copolymer or by exciplex formation in the naphthalene–dimethylaniline diblock copolymer. Upon incorporation of an intervening block derived from pentamethylphenylethylisocyanide 8, exciplex formation is suppressed in the related triblock copolymer. Transient absorption spectra of this family of di- and triblock copolymers reveal the formation of radical ion pairs, with a lifetime of 1.1 μs in the anthracene–dimethylaniline diblock copolymer.