Journal of the American Chemical Society, Vol.142, No.4, 2059-2067, 2020
Axially Chiral Spiro-Conjugated Carbon-Bridged p-Phenylenevinylene Congeners: Synthetic Design and Materials Properties
Spiro-conjugated systems are attracting considerable interest for their chiroptical properties and because of their compact structure the small reorganization energy upon electronic excitation or ionization. We report here a modular and convergent synthesis of axially chiral spiro-conjugated carbon-bridged p-phenylenevinylenes (spiro-CPVs) in a racemic and optically active form where two carbon-bridged p-phenylenevinylene molecules are connected by a spiro carbon atom. Our synthetic design focuses on the C-2 symmetry of the spiro-CPV molecules, relying on coupling of two 3-lithio-2-arylindene molecules on a carbon monooxide molecule that serves as the Spiro carbon center in the target molecule. We prepared derivatives including those possessing phenol groups that facilitate optical resolution and also serve as a platform for the synthesis of a variety of optically active derivatives, which exhibit circularly polarized photoluminescence with high fluorescence quantum yields, large dissymmetry factors, and high photostability. For example, a bis(phenylethynyl) derivative exhibited a fluorescence quantum yield of 0.99 and a dissymmetry factor in luminescence of vertical bar g(lum)vertical bar = 2.7 X 10(-4), values highest among and comparable to those of reported CPL compounds, respectively. A tetrakis-diarylamine derivative shows hole mobility (mu(h) = 3.84 X 10(-5) cm(2) V-1 s(-1); space charge-limited current measurement of a spin-coated film) comparable to that of a popularly used hole-transporting material, spiro-OMeTAD (mu(h) = 2.6 X 10(-5) cm(2) V-1 s(-1)), as well as high thermal and phase stability (T-5d = 382 degrees C, T-g = 171 degrees C).