Toward pi-conjugated molecule bundles: synthesis of a series of B,B',B''-trianthryl-N,N',N''-triarylborazines and the bundle effects on their properties.

As a prototype of a pi-conjugated molecule bundled system, a series of B,B',B''-trianthryl- N,N',N''-triarylborazine derivatives bearing various p-substituted phenyl groups (p-R-C(6)H(4): R = hexyl (1), i-Pr (2), CF(3) (3), Br (5)) as aryl groups was designed and synthesized. The crystal structure analysis of these derivatives confirmed that the three anthryl and three phenyl groups are bundled up alternately in a C(3) symmetrical gear-shaped fashion. On the basis of this structure, the trianthrylborazine derivatives form a unique honeycomblike packing structure consisting of intermolecular pi-stacking of the anthryl moieties. Significant bundle effects were observed in the photophysical and electrochemical properties of these compounds. In their fluorescence spectra, the trianthrylborazine derivatives (1-3) show intense emissions around 390 nm, whose quantum yields (1, Phi(F) = 0.62; 2, Phi(F) = 0.59; 3, Phi(F) = 0.63) are about twice high as that of anthracene (Phi(F) = 0.27). The cyclic voltammetry measurements show that the oxidation peak potential can be tuned by varying the substituents on the phenyl moieties. Theoretical calculations (B3LYP/ 6-31G(d)) suggested that secondary through-bond/through-space interactions in the bundled structure play an important role in the tuning of these properties. Facile structural derivatization at the 10-position of the anthryl moieties of trianthrylborazine was conducted to demonstrate the utility of the borazine skeleton as a core framework for new organic electronic materials.