Time-resolved difference absorption spectra of J-aggregates in ethyleneglycol/water glass were measured by femtosecond pump- probe spectroscopy. the induced absorption near the J-band at 20 K was assigned to the transitions from n-exciton states to (n $PLU 1)-exciton states (n $GREQ 1). The decay time of the n($GREQ 2)-exciton states is determined to be about 200 fs. For applications of the J-aggregates as nonlinear optical deices, we present a new fabrication method, called vertical spin-coating, to prepare highly oriented 1D J-aggregates dispersed in polymer films. The films are stable even at room temperature. Linear dichroic spectra of the oriented J-aggregate of 1,1'-diethyl- 2,2'-quinocyanine bromide were measured. The dichroic ratio at the peak of J-band was 5 to 10, depending on the preparation conditions. Precise measurement of the dichroism at the J-band revealed that the J-band is composed of two bands with transition dipole moment perpendicular to each other. Large change in a static dipole moment upon electronic excitation was unexpectedly observed in the oriented J-aggregates by electromodulation spectroscopy. The difference absorption spectra due to the Kerr effect were induced by changes in a static dipole moment and a polarizability. The change in the static dipole moment associated with the transition from the ground state to the exciton state were measured with the applied AC field of Hz and the polarization parallel and perpendicular to the 1D axis of the oriented J-aggregates.
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