Exciton dynamics in disordered linear chains of poly(di-n-hexylsilane): Experiment and theory

We have measured the absorption, luminescence, luminescence excitation spectra, and time response of the luminescence intensity of poly(di-n-hexylsilane) (PDHS) film and of low-temperature glass of dilute PDHS solution at 2 K. It is found that the luminescence peak energies shift with the excitation energy below 3.385 +/-0.005 eV for the film and below 3.463+/-0.005 eV for the glass, and that the rise and decay times of luminescence intensity at the peak energies are 70 and 300 ps, respectively, for the film, and 130 and 260 ps, respectively, for the glass. In order to explain these results, numerical diagonalization of the one-dimensional Frenkel exciton Hamiltonian with disorder is carried out, and the luminescent process is formulated with the assumption that the exciton does not change the site by phonon scattering. We estimate the transition-dipole moment to be mu(0)=3.0x10(-18) esu cm for the film and mu(0)=4.2x10(-18) esu cm for the glass and the transition constant to be c(tr)=1.9x10(12) s(-1) for the film and c(tr)=0.4x10(12) s(-1) for the glass. We discuss the role of hidden structures at the low-lying exciton states that appear in the site representation of exciton wave functions. The hidden structure correlates the microscopic picture with the phenomenological;segment model. It is found that the long-range dipole-dipole interaction contributes to the long luminescence rise time.