Narrow Results

Optimized geometries and vibrational frequencies of polydiacetylenes (PDAs) and their derivatives were studied by density functional calculations at the B3LYP/6-31G* level. The time-dependent density functional theory was used to determine their vertical transition energies and corresponding oscillator strengths. Calculations show that different side groups in these linear carbon chains can significantly modify their structural and electronic properties, whereas the effect of terminal substitution is negligible. Predicted equilibrium geometries indicate that the single, double, and triple bonds of PDAs and their derivatives are almost unchanged as the chain increases, showing a remarkable character of localized bond. The periodic boundary condition calculations reveal that the strongest adsorption for the infinite chain of PDA appears at 723 nm, and the HOMO → LUMO excitation is responsible for this strong electronic transition.