Two-photon spectroscopy of π-conjugated polymers:: The case of poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS)

The two-photon fluorescence excitation and optoacoustic spectra of red polyDCHD-HS in benzene solution at room temperature have been investigated in the 1600-750 nm exciting wavelength region (effective two-photon energy similar to1.55-3.31 eV). The spectra obtained by the two detection techniques are of comparable accuracy, and the observed band profiles are in good agreement. Two electronic band systems have been observed and assigned to two-photon allowed A(g) --> A(g) transitions. Both A(g) states are at energies higher than that of the strongly one-photon allowed 1B(u) state. An estimate of the absolute two-photon absorptivity of polyDCHD-HS at 406.0 nm (similar to3.05 eV) is given by means of the optoacoustic method. Our results are discussed on the basis of the current theories on electronic states of pi -conjugated polymers and compared with reported data on these systems.