The absorption spectra of the p-phenylene-ethynylene（p-PPE） oligomers（up to n = 12） were estimated by DFT and TD-DFT methods. The effective conjugation length（ECL） of the corresponding polymer was obtained by ex...The absorption spectra of the p-phenylene-ethynylene（p-PPE） oligomers（up to n = 12） were estimated by DFT and TD-DFT methods. The effective conjugation length（ECL） of the corresponding polymer was obtained by extrapolating the first excitation energies of the oligmers to infinite chain length with an alternative exponential function. The absorption spectral red-shift mainly depends on the ？-conjugation segment of oligomers resulting from the planarization of the backbone. The excitation mechanism of the rotamer has been investigated sufficiently by analyzing the orbital density variation upon the conformational rotations around the cylindrical triple-bonded carbon which is believed to impact significantly on the optical spectrum. The calculated results further indicate that rotation about the cylindrical triple bond interrupts the conjugation of rod-like oligomers to lead an angle-dependence of the corresponding excitation energy. The results are helpful to interpret the conformational-dependent spectroscopic phenomena of p-phenyleneethynylene and derivatives oligomers and polymers observed in ensemble and single molecule spectroscopy.展开更多
基金supported by the National Natural Science Foundation of China(21373012)the Key Project of Educational Committee of Anhui Province(KJ2010A143)
文摘The absorption spectra of the p-phenylene-ethynylene（p-PPE） oligomers（up to n = 12） were estimated by DFT and TD-DFT methods. The effective conjugation length（ECL） of the corresponding polymer was obtained by extrapolating the first excitation energies of the oligmers to infinite chain length with an alternative exponential function. The absorption spectral red-shift mainly depends on the ？-conjugation segment of oligomers resulting from the planarization of the backbone. The excitation mechanism of the rotamer has been investigated sufficiently by analyzing the orbital density variation upon the conformational rotations around the cylindrical triple-bonded carbon which is believed to impact significantly on the optical spectrum. The calculated results further indicate that rotation about the cylindrical triple bond interrupts the conjugation of rod-like oligomers to lead an angle-dependence of the corresponding excitation energy. The results are helpful to interpret the conformational-dependent spectroscopic phenomena of p-phenyleneethynylene and derivatives oligomers and polymers observed in ensemble and single molecule spectroscopy.
