The development of low band gap conjugated materials has been an area of intense scientific research due to the possible commercial application of these materials in organic field effect transistors (OFETs), organic light-emitting diodes (OLEDs) and photovoltaic cells (OPV).1 A well exploited strategy to accesses these low bang gap materials has been the synthesis of donor-acceptor (D-A) π-conjugated systems. A low band gap resulting from a low LUMO level, whilst maintaining a deep HOMO level is a desirable characteristic of such materials. Coordination of a Lewis acid to a basic site of an acceptor unit (e.g.,Benzothiadiazole) of the D-A systems results in a significant decrease in the energy of the LUMO levels.2 However, the principle drawback of this Lewis acid binding strategy is that these systems are moisture and Lewis base sensitive which both cleave the acceptor→Lewis acid dative bond.2 A method for enhancing the stability of the coordinated Lewis acid system is by coupling dative bond formation with C-B bond formation to form a fused C-N chelated Lewis acid adduct.3 This methodology has the additional benefit of locking the neighboring aromatic units co-planar into a fully fused structure, further enhancing the effective conjugation length. Herein we report the synthesis and photo-physical properties of a series of partially fused and fully fused structure. These compounds have reduced LUMO energies, high stability, demonstrate very large stokes shifts and show intense Red / NIR emission in the solid state.
1 K. Colladet, S, Fourier, T. J. Cleij, L. Lutsen, J. Gelan, D. Vanderzande, L.
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