Migratory Shift in Oxidative Cyclodehydrogenation Reaction of Tetraphenylethylenes Containing Electron-Rich THDTAP Moiety.

Four tetraphenylethylenes (2a-d) containing an electron-rich 2,3,4,6-tetrahydro-1,6-dithia-3a-azaphenalene (THDTAP) moiety have been synthesized. The 2a-d show aggregation-induced emission (AIE) with yellowish green photoluminescence (PL) in THF-H2O (v/v, 1:9) solution and in the solid state. Compounds 2a-d undergo 1,2-migratory shift in oxidative cyclodehydrogenation reactions to afford the unexpected products 3a-d which display green PL in CH2Cl2 solution and are non-emissive in the solid state. The PL intensities of 3a-d are clearly enhanced in the presence of meta-chloroperoxybenzoic acid (mCPBA) owing to the oxidation of the S-atoms on the THDTAP moiety. In contrast, the PL of 2a-d in THF-H2O (v/v, 1:9) solution is quenched by adding mCPBA, ascribable to the oxidation of the C=C bond on the ethylene moiety. It is found that the absorption of 3a-d is distinctly red-shifted from the UV/Vis region to the NIR region upon acidification, arising from the protonation of the N-atom on the THDTAP moiety. Furthermore, 3a-d display nonlinear optical response (NLO) and optical limiting (OL) behaviour which is superior to that of the well-known OL material C-60.