Journal of the American Chemical Society, Vol.127, No.42, 14859-14866, 2005
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-C6H4: R = hexyl (1), i-Pr (2), CF3 (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/6-31 G(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.