Triplet state spectroscopy of σ-conjugated poly[methyl(phenyl)silylene]

Steady-state and time-resolved photoluminescence of poly[methyl(phenyl)silylene] (PMPSi) in solutions and films, and films doped with acetophenone, biphenyl and naphthalene were studied in the temperature range 5-77 K. It was found that the steady-state, prompt and delayed luminescence spectra of PMPS in solutions and solid films are similar under the same excitation and registration conditions. The delayed luminescence spectrum is represented by broad, unsymmetrical and structureless band with maximum at ca. 450 and 465 nm in PMPSi solution and film, respectively. The decay time of this emission, which was assigned to the intrinsic phosphorescence of PMPSi, was found to be within the microsecond time domain; at 77 K it could be observed with the delay time up to 30 μs with respect to excitation pulse. Quite effective triplet-triplet energy transfer was observed. The results indicate that the energy of the lowest triplet state is considerably lower than the energy of the lowest excited singlet state, which involves a strong correlation of Si-Si σ-electrons of the polymer backbone, and can be described in the concept of Frenkel exciton. It was also demonstrated that the vibronic structure of the long-lived emission reported in literature for PMPSi films is most probably due to the presence of chemical defects and impurities and it does not represent the intrinsic feature of the PMPSi triplet.