Toru Inaba

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

Abstract 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), anhydrorhodovibrin ( n =12) and spirilloxanthin ( n =13).

Excited-state dynamics among the 1Bu+, 1Bu− and 2Ag− states of all-trans-neurosporene as revealed by near-infrared time-resolved absorption spectroscopy

Abstract Subpicosecond time-resolved absorption spectra in the 840–1040 nm region were recorded for all-trans-neurosporene in nonpolar solvents having different polarizabilities, and analyzed by means of singular-value decomposition (SVD) and subsequent global fitting using sequential models. In n-hexane, n-pentadecane and benzene, (a) transient absorption and stimulated emission from the 1Bu+ state and (b) transient absorption from the 1Bu− state were identified as major components. In carbon disulfide, (c) transient absorption from the 2Ag− state was clearly identified as an additional component. The results have confirmed the sequential internal conversion processes of 1 B u + → 1 B u − → 2 A g − .

Sub-picosecond time-resolved absorption spectroscopy of all-trans-neurosporene in solution and bound to the LH2 complex from Rhodobacter sphaeroides G1C

Abstract Sub-picosecond, time-resolved absorption spectra of all- trans -neurosporene, both free in n -hexane solution and bound to the LH2 complex from Rhodobacter sphaeroides G1C, were recorded and analyzed by singular-value decomposition followed by global fitting using a sequential model. The former experiment identified the 1B u + →1B u − →2A g − internal conversion, whereas the latter experiment identified a transformation of 1B u + →2A g − →T 1 (1 3 B u + ). Excitation to the 1B u + (0) or 1B u + (1) vibronic level resulted in enhancement of stimulated emission from the particular level, showing that vibrational relaxation in the 1B u + state has a time constant comparable to, or larger than, that of electronic relaxation.

The role of the newly-found 1Bu− state of carotenoid in mediating the 1Bu+-to-2Ag− internal conversion and the excited-state dynamics of carotenoid and bacteriochlorophyll in a bacterial antenna complex

Abstract Most recent finding of the 1B u − state of carotenoids in-between the 1B u + and 2A g − states by measurements of resonance-Raman excitation profiles, and that of the 1B u + →1B u − →2A g − internal-conversion processes by visible and near-infrared time-resolved absorption spectroscopy are reviewed for all- trans -neurosporene both free in solution and bound to the LH2 antenna complex from Rhodobacter sphaeroides G1C. The excited-state reactions between carotenoid (Car) and bacteriochlorophyll (BChl) a in the LH2 complex, including the singlet hetero-fission between them and the Car-to-BChl singlet-energy transfer, both probed by time-resolved absorption spectroscopy, are also summarized.