Low frequency modes of surface adsorbed dye molecules studied by optical high resolution techniques

We observed for the first time in an optical high resolution experiment (fluorescence line narrowing) the coupling of low frequency adsorbate motions to vibronic bands of the electronic transition of quinizarin adsorbed on γ-alumina. These motions may provide an important dephasing mechanism for the electronic excitation of absorbed molecules. The increased hole width of adsorbed dyes which is several times larger than in amorphous hosts is thought to be caused by these low frequency modes.