Ultrafast relaxation kinetics of excited states in a series of mini- and macro-β-carotenes -: art. no. 174302

Relaxation kinetics in a series of all-trans-carotenes that have excited states with different energies has been investigated using femtosecond absorption and Raman spectroscopy. The dependence on the energies shows that the 1B(u)(-) state plays an intermediate state of the relaxation from the initially photoexcited 1B(u)(+) state to the 2A(g)(-) state. After the relaxation to the 2A(g)(-) state, the excess energy is held in a C=C stretching mode (nu(1)) of the 2A(g)(-) state. The lifetime of the nu(1) mode is longer than several picoseconds in short (mini) carotenes, but it is shorter than 1 ps in long (macro) carotenes. Vibrational feature in carotenoids is of importance in energy transfer of photosynthesis, because the excess energy of the photoexcitation is stored in the nu(1) mode during the relaxation kinetics.