Laura Foglia, Lea Bogner, Martin Wolf, Julia Stähler:
arXiv: 1412.0597 [cond-mat.mtrl-sci], (2014), pp 10;
We present a systematic study of the exciton population dynamics at the interface of the spirobifluorene derivative 2,7-bis(biphenyl-4-yl)-2',7'-ditertbutyl-9.9'-spirobifluorene (SP6) and the non-polar(1010) surface of ZnO, using time-resolved excited state optical transmission spectroscopy. The photoexcited dye first undergoes intramolecular vibrational relaxation in the S1 state on a 2 to 9 ps timescale. Subsequently, the excited state transmission reveals transitions from two distinct vibrational levels of S1, with a lifetime of the vibrationally excited state that is comparable to the one of the vibrational ground state (vGS). The electronic population relaxes by (i) decay to the electronic ground state (ii) transfer to a long-lived dark state that remains populated for longer than 5 microseconds, and (iii) diffusion-limited charge transfer to the ZnO conduction band. Remarkably, the lifetime of the vibratioanlly trapped excition (exciton-vibron) and vGS exciton are not equally affected by a change of substrate. Our observations strongly suggest a shorter diffusion length of the exciton-vibron and strong electronic-nuclear coupling of optically excited molecules.
The original publication is available by link arXiv: 1412.0597