Optical properties such as photoluminescence (PL) and electro luminescence (EL) of poly(diphenylacetylene)(PDPA) derivatives with substituents containing silicon and germanium atoms have been studied. PDPA derivatives exhibited highly efficient PL and PL spectral narrowing originated from amplified spontaneous emission (ASE) in the case of high excitation. The peak wavelength of PL spectra depends on the positions of substitution and the atoms(silicon or germanium) of the substitution. EL has also been observed from PDPA derivatives sandwiched between magnesium-silver alloy cathode and indium-tin-oxide anode. PL decay has also been confirmed to be dependent on the position of the substituents and the hetero-atoms in the substituents. These ...