A diphenylacetylene monomer carrying a dimesitylboryl functional group was newly synthesized and polymerized by heating the toluene solution at 80 degrees C, using TaCl5-n-Bu4Sn as a catalyst. A polydiphenylacetylene (PDPA) derivative was obtained in high yield despite the presence of the heteroatom; the polymer had an extremely high weight-average molecular weight of 1.27 x 10(6) gmol(-1) and readily dissolved in organic solvents. This polymer was highly resistant to heat and existed in an amorphous, glassy state at room temperature. Unlike the usual PDPA derivatives, the fluorescence (FL) maximum for this derivative appeared at 526 nm through efficient intramolecular energy transfer from the side dimesitylboryl groups to the polyene backbone upon excitation at a very short wavelength of 320 nm, indicating an extremely large Stokes shift of 206 nm. Moreover, the polymer showed considerably higher FL efficiency of 49.3% in a tetrahydrofuran solution and 19.1% in a film as compared to the usual PDPA derivatives. This polymer reacted with fluoride ions to exhibit critical changes in absorption and FL emission, which were expressed by an exponential and a Gaussian functional equation, respectively. (C) 2018 Elsevier Ltd. All rights reserved.