The lipid-rafts hypothesis proposes that naturally occurring lipid aggregates exist in the plane of membrane that are involved in signal transduction, protein sorting, and membrane transport. To understand their roles in cell biology, a direct visualization of such domains in living cells is essential. For this purpose, 6-dodecanoyl-2-(dimethylamino)naphthalene (laurdan), a membrane probe that is sensitive to the polarity of the membrane, has often been used. We have synthesized and characterized 6-dodecanoyl-2-[N-methyl-N-(carboxymethyl)amino]naphthalene (C-laurdan), which has the advantages of greater sensitivity to the membrane polarity, a brighter two-photon fluorescence image, and reflecting the cell environment more accurately than laurdan. Lipid rafts can be visualized by two-photon microscopy by using C-laurdan as a probe. Our results show that the lipid rafts cover 38 % of the cell surface.

Optical activity is the result of chiral molecules interacting differently with left versus right circularly polarized light. Because of this intrinsic link to molecular structure, the determination of optical activity through circular dichroism (CD) spectroscopy has long served as a routine method for obtaining structural information about chemical and biological systems in condensed phases. A recent development is time-resolved CD spectroscopy, which can in principle map the structural changes associated with biomolecular function and thus lead to mechanistic insights into fundamental biological processes. But implementing time-resolved CD measurements is experimentally challenging because CD is a notoriously weak effect (a factor of 10(-4)-10(-6) smaller than absorption). In fact, this problem has so far prevented time-resolved vibrational CD experiments. Here we show that vibrational CD spectroscopy with femtosecond time resolution can be realized when using heterodyned spectral interferometry to detect the phase and amplitude of the infrared optical activity free-induction-decay field in time (much like in a pulsed NMR experiment). We show that we can detect extremely weak signals in the presence of large achiral background contributions, by simultaneously measuring with a femtosecond laser pulse the vibrational CD and optical rotatory dispersion spectra of dissolved chiral limonene molecules. We have so far only targeted molecules in equilibrium, but it would be straightforward to extend the method for the observation of ultrafast structural changes such as those occurring during protein folding or asymmetric chemical reactions. That is, we should now be in a position to produce 'molecular motion pictures' of fundamental molecular processes from a chiral perspective.

Synthesis and physical properties of novel multibranched two-photon materials are reported. The compound with three units of 4-(p-diphenylaminostyryl)-2,5-dicyanostyryl moieties attached to the central triphenylamine core exhibits a very large two-photon absorption cross-section.

[Structure: see text] Anthracene derivatives with a variety of donor-acceptor substituents have been synthesized and shown to exhibit large two-photon cross sections over a wide range of wavelengths.

Molecular polarizabilities and hyperpolarizabilities of a series of octupolar molecules that are donor-substituted triphenylmethane dyes are calculated. The four-state model of an octupolar molecule is used to describe the nonlinear optical properties of this type of molecules. As the charge-transfer character of the ground state is increased by using a strong donor, both the molecular polarizability and first hyperpolarizability increase monotonically. These patterns are in strong contrast with those exhibited by the linear push−pull polyene. On the basis of these results, it is suggested that a common strategy to maximize the molecular polarizability can also be used to optimize the first hyperpolarizability in the case of octupolar molecules such as triphenylmethane dyes.

A series of 9,10-bis(arylethynyl)anthracene derivatives (1-8) have been synthesized and their two-photon absorption (TPA) cross sections were measured by nanosecond fluorescence measurement and femtosecond Z-scan methods. The λ max values of these molecules are very similar and the λ max (2) values are near 800 nm. The δ max ns /MW of the dipole increases with the conjugation length, whereas those for the quadrupoles decrease slightly with MW. Also, the δ max ns /MW of the octupole is smaller than the dipole. In all cases, δ max ns /MW of the quadrupoles are larger than the dipoles. Moreover, the results of the femtosecond Z-scan experiment indicate significant contribution by the excited-state absorption in δ max ns . Noteworthy is the good agreement between the structure-TPA property relationships determined by both methods.

A theoretical description of the molecular polarizability (α) and first and second hyperpolarizabilities (β and γ) of a guanidinium-type octupolar molecule is presented. By using a valence bond and three charge-transfer states with nonzero transfer integrals, the electronic states are obtained as linear combinations of these basis states. It is found that a doubly degenerate excited state is only optically coupled to the ground state. Based on the analytic expressions for α, β, and γ obtained, it is shown that the resultant tensor elements of β satisfy the symmetry requirements of point group D3h. Unlike the linear push–pull polyenes, the magnitudes of α, β, and γ of the guanidinium-type octupolar molecules increase as the charge-transfer character of the electronic ground state increases. Also, their dependences on the distance (d) between the donor and acceptor are briefly discussed.

A two-photon sensor for the metal ions derived from azacrown ether as the receptor is reported. The sensor emits strong two-photon fluorescence when excited by 800 nm laser photons. Moreover, the binding constants measured by the one- and two-photon fluorescence are similar. This result may be useful for the design of efficient two-photon fluorescence probes for biological substrates.