Large optical nonlinearity has attracted much attention for applications in optical devices. A very large enhancement of third order optical nonlinearity of π-conjugated molecules can be realized without a major redshift of the absorption spectrum that disturbs optical transparency in the visble region.

Left pannel: The second molecular hyperpolarizability and phase spectra measured and simulated in β-carotene and its homologs having different conjugation double bonds n. (a) C30 (n=7), (b), C36 (n=9), (c) β-carotene C40 (=11), (d) C44 (n=13), and (e) C50 (n=15).

reference
(1) Fujiwara et al., Phys. Rev B, 78 (2008) 161101

Ultrafast spectroscopy in photosynthetic pigments

Third and fifth order nonlinear optical signals from all-trans-β-carotene using ultrashort laser pulses

In our laboratory, ultrafast excited state dynamics of photosynthetic pigments, carotenoids and (bacterio) chlorophylls, are investigated by ultrafast spectroscopic measurements, e.g. four-wave mixing, pump-probe, time-resolved fluorescence techniques.

reference
sub-20 fs four wave mixing spectroscopy
　(1) Sugisaki et al., Phys. Rev B, 75 (2007) 155110
　(2) Fujiwara et al., Phys. Rev B, 77 (2008) 205118
　(3) Sugisaki et al., Phys. Rev B, 80 (2009) 035118
　(4) Sugisaki et al., Phys. Rev B, 81 (2010) 245112
100 fs pump-probe spectroscopy
　(1) Kosumi et al., Chem. Phys. Lett., 483 (2009) 95
　(2) Kosumi et al., Angew. Chem. Int. Ed., 50 (2011) 1097
　(3) Kusumoto et al., J. Phys. Chem. A, 115 (2011) 2110

Artificial photosynthetic membrane and light-harvesting antenna complexes

Hybrid photosynthetic units using peripheral and core antennae

A series of carotenoids reconstituted in to light-harvesting antenna 1 complex

Nonlinear optical properties of photosynthetic pigments

Third order harmonic generation in β-carotene and its homologs

Electroabsorption spectroscopy Electroabsorption (Stark) spectroscopy is one of the most promising methods to probe the electrostatic interactions in the pigment protein complexes since applied electric-field perturbs electrostatic potential around the pigments and thus induced subtle chnage of the absorbance of the pigments can be detected effectively by this particular technique. We applied this technique to elucidate the electrostatic interaction in the LH1 and LH2 complexes, RC, and carotenoids in polymer matrix. reference (1) Yanagi et al., Phys. Rev. B, 67 (2003) 115122 (2) Yanagi et al., Phys. Rev. B, 69 (2004) 205103 (3) Yanagi et al., Phys. Rev. B, 71 (2005) 195118 (4) Yanagi et al., J. Phys. Chem. B, 108 (2004) 10334 (5) Yanagi et al., J. Phys. Chem. B, 109 (2005) 992 (6) Nakagawa et al., J. Phys. Chem. B, 112 (2008) 9467 (7) Kusumoto et al., Chem. Phys., 373 (2010)