Masahiro Kotani

We report results of single Molecule study of phosphorescent organometallic complex, tris(2-phenylpyridine)-iridium (Ir(ppy)(3)). Single molecule emission intensities show a wide multi-component distribution. Photobleaching times of molecules emitting with particular intensity are exponentially distributed. The dependence of the inverse of the mean photobleaching time on the emission intensity reveals linear dependence for lower intensities and more complex behavior for higher intensities. The results obtained on Ir(ppy)(3) are compared with those of a fluorescent label, diethyloxacarbocyanine. (C) 2004 Elsevier B.V. All rights reserved.

We present a simple and straightforward method for determining absolute spatial orientations of transition dipole moments of single fluorescent molecules. Far-field polarization microscopy provides angles of the dipole moments projected in the plane of the sample. Optical field near total internal reflection surfaces has a strong component perpendicular to the sample and, for a given in-plane angle, provides unambiguous orientation of the molecular dipole moment. Experimentally, both excitation modes are alternated to monitor real-time conformational dynamics of tetramethylrhodamine molecules covalently attached to a quartz substrate. (C) 2003 American Institute of Physics.

Molecular orientation in thin films of methylene blue, prepared by dip-coating. has been studied by UV-visible absorption spectroscopy and X-ray diffraction. In multilayered films the molecules are essentially standing normal to the surface of a fused quartz substrate and form a layered structure with a periodicity that corresponds to the molecular length. Due to this arrangement the film is only faintly colored, since, with normal incidence, the electric field of the incident light is orthogonal to the transition moment of the molecules, This structure can be formed by self-organization in the course of drying. not by epitaxy. (C) 2001 Elsevier Science B.V. All rights reserved.

Molecular orientation in thin films of methylene blue, prepared by dip-coating. has been studied by UV-visible absorption spectroscopy and X-ray diffraction. In multilayered films the molecules are essentially standing normal to the surface of a fused quartz substrate and form a layered structure with a periodicity that corresponds to the molecular length. Due to this arrangement the film is only faintly colored, since, with normal incidence, the electric field of the incident light is orthogonal to the transition moment of the molecules, This structure can be formed by self-organization in the course of drying. not by epitaxy. (C) 2001 Elsevier Science B.V. All rights reserved.

Molecules can be oriented when they are adsorbed onto a solid surface with an appropriate surface structure. Examples are shown which illustrate a unidirectional alignment. 4-Dimethylamino-4'-nitrostilbene (DMANS) exhibits an oriented adsorption when evaporated onto a cleaved face of a glycine single crystal. The same compound exhibits also a high degree of orientational order when an evaporated film of the compound is mechanically brushed in a direction. The mechanism of the molecular alignment is discussed based on the results of polarized optical absorption, optical second-harmonic generation, X-ray diffraction and scanning force microscopy. (C) 2000 Elsevier Science S.A. All rights reserved.

Weak fluorescence from the second excited state of an anthracene crystal has been observed by two-step excitation via the lowest excited state. Relaxation processes of a highly excited state to the lowest state are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

Biphotonic emission of electrons has been observed when a crystal of aromatic hydrocarbon, coronene or alpha-perylene, is excited at 3.49 eV (lambda = 355 nm). Measurements using a pair of pulses with variable intervals show that an intermediate state is involved which has a lifetime in the nanosecond range. The lifetime, however, is shorter than the fluorescence lifetime, indicating that excitons in the surface region can have a shorter lifetime compared to the bulk excitons. Depending on the material and also on the excitation energy, mutual annihilation or photoionization of surface excitons is responsible for the electron emission. (C) 1998 Elsevier Science B.V. All rights reserved.

Weak fluorescence from shea-lived excited states in anthracene crystals has been observed with optical excitation at lambda = 254 nm (4.89 eV). The lifetime of the second excited state is estimated to be 0.1 ps. (C) 1998 Elsevier Science B.V. All rights reserved.

Modulation of fluorescence from a perylene single crystal by a magnetic field has been studied with excitation in the VUV and with X-ray excitation. It has been concluded that fission of highly excited singlet state into a triplet pair dominates the modulation in the case of VUV excitation, whereas with X-ray excitation fusion of triplet excitons, generated by secondary electrons, plays an important role.