Two different pathways of internal conversion in carotenoids depending on the length of the conjugated chain

Near-infrared, subpicosecond time-resolved absorption spectroscopy of all-trans carotenoids having the number of conjugated double bonds, n = 9-13, identified two different pathways of internal conversion in accordance with the energy diagram recently determined by measurements of resonance-Raman excitation profiles (RREPs) [K. Furuichi, T. Sashima, Y. Koyama, Chem. Phys. Lett. 356 (2002) 547]: the 1B(u)(+) --> 1B(u)(-) --> 2A(g)(-) internal conversion for neurosporene (n = 9) and spheroidene (n = 10), whereas the 1B(u)(+) --> 3A(g)(-) -->2A(g)(-) internal conversion for lycopene (n = 11), anhyodrorhodovibrin (n = 12) and spirilloxanthin (n = 13). (C) 2003 Elsevier Science B.V. All rights reserved.