Oxidative cyclization of bis(biaryl)acetylenes: synthesis and photophysics of dibenzo[g,p]chrysene-based fluorescent polymers.

Annelation of π-conjugated frameworks has proved to be an effective way to enhance conjugation in π-conjugated polymers by eliminating conformational disorder. Upon the basis of this approach a number of ladder polymers having small band gaps and intense fluorescence have been developed.1-3 Similarly isolated fused polycyclic aromatics also serve as attractive building units.4 Considering their rigid structures and symmetrically forbidden or weakly allowed transitions,5 the incorporation of these units into π-conjugated main chains would realize unique fluorescence properties such as small Stokes shifts and extended excited-state lifetimes. These features may allow for long-range, through-bond exciton migration, a key requisite for amplified sensing of ultra-trace analytes such as 2,4,6-trinitrotoluene (TNT),6 using the molecular-wire approach.7,8 As a proof of this concept, we have recently reported investigations of a series of triphenylene-based polymers.9 As an extension, we have been interested to incorporate dibenzo[g,p]chrysene, recognized as a benzeno-annelated stilbene, into conjugated polymers. However, the conventional routes to this skeleton have been limited to only a few types of classical syntheses.10 We report herein a conceptually new oxidative acetylene cyclization method that provides a facile and versatile route to dibenzo[g,p]chrysenes and a demonstration of the utility of the chromophore in the design of novel π-conjugated polymers. Our group has previously reported powerful routes to fused polycyclic aromatics as shown in eq 1, where the electrophilic 6-endo mode cyclization directed by electron-donating substituents provides a variety of phenanthrene derivatives.11 To construct a dibenzo[g,p]chrysene skeleton, we have extended this scheme to a double intramolecular cyclization as shown in eq 2. The