“…In addition, carotenoids are also potential candidates for molecular wires, 34 and perturbing their conductivity by SPPs can reveal new aspects from it. 35 In contrast to other dye molecules utilized in SPP studies, carotenoids show a strong electron correlation, a rather complicated excited state structure and short excited state lifetimes, and thus low fluorescence yield. Since the transition to the first excited state S 1 (with symmetry group of 2 1 A g ) is forbidden due to the molecule symmetry, the conventional absorption and fluorescence spectroscopy observes transitions involving second excited state of carotenoids, conventionally called S 2 (1 1 B u ).…”