Identification of the optically active vibrational modes in the photoluminescence of MEH-PPV films

Abstract

The temperature dependence of the photoluminescence properties of a thin film of poly[2-methoxy-5-(2(')-ethylhexyloxy)-p-phenylene-vinylene], MEH-PPV, fabricated by spin coating, is analyzed. The evolution with temperature of the peak energy of the purely electronic transition, of the first vibronic band, of the effective conjugation length, and of the Huang-Rhys factors are discussed. The asymmetric character of the pure electronic transition peak and the contribution of the individual vibrational modes to the first vibronic band line shape are considered by a model developed by Cury et al. [J. Chem. Phys. 121, 3836 (2004)]. The temperature dependence of the Huang-Rhys factors of the main vibrational modes pertaining to the first vibronic band allows us to identify two competing vibrational modes. These results show that the electron coupling to different vibrational modes depends on temperature via reduction of thermal disorder.

Temperature dependence of intra‐chain photoluminescence of a long oligothiophene

“…It has been explained to be attributed to reduction in the conjugation length of the polymer chain that is caused by conformational disorders due to thermal motions of some moieties in the chain [13][14][15][16][17]. This is expected to hold also for the present 16T sample [18].…”

“…A blueshift of the optical spectra with increasing temperature has been well documented for conjugated polymers [13][14][15][16][17]. It has been explained to be attributed to reduction in the conjugation length of the polymer chain that is caused by conformational disorders due to thermal motions of some moieties in the chain [13][14][15][16][17].…”

Intrachain photoluminescence dynamics of a long oligothiophene at room temperature

“…The vertical broken line in the figure demonstrates that the absorption spectra blueshift with increasing temperature, similarly to the PL spectra. A blueshift with increasing temperature in the optical spectra of conjugated polymers has been explained by being due to reduction in the conjugation length of the polymer chain caused by thermally induced conformational disorders [13][14][15][16][17]. This is expected to hold for the present 16 T sample as well [18].…”

Optically active vibrational modes in the photoluminescence line shape of BDMO-PPV films

“…It was also possible to observe that for BEH-PPV [13] using three modes, as well as for MEH-PPV [17] using four modes, the fits are bad in the intermediate region between the peak associated with the purely electronic transition and that associated with the first vibronic band (range of 1.95 to 2.05 eV, at 12 K), passing below the experimental curve. This deficiency occurs independently of the value for parameter A.…”

“…In the recent work, using the four main modes cited to fit the line shape of PL of the MEH-PPV deposited on Cu, da Silva et al [17] showed that the adjustments for this material had low sensitivity to the parameter A. It was also possible to observe that for BEH-PPV [13] using three modes, as well as for MEH-PPV [17] using four modes, the fits are bad in the intermediate region between the peak associated with the purely electronic transition and that associated with the first vibronic band (range of 1.95 to 2.05 eV, at 12 K), passing below the experimental curve.…”