The ultrafast photodynamics of porphyrin-fullerene dyads in which the distance between the porphyrin and C 60 moieties is varied systematically at close proximity has been examined using fluorescence up-conversion and pump-probe transient absorption techniques with time resolutions of ca. 100 fs. The porphyrin-fullerene dyads examined are MP-D-C 60 (M ) Zn and 2H) in which the C 60 moiety is directly connected with the porphyrin ring at the meso position and MP-O-C 60 , MP-M-C 60 , and MP-P-C 60 in which the C 60 moiety is linked with porphyrin moieties through the benzene ring at the ortho, meta, and para positions, respectively. The charge transfer (CT) bands are observed for MP-D-C 60 and MP-O-C 60 , whereas no CT band is seen for MP-M-C 60 and MP-P-C 60 . Time-resolved absorption spectral measurements indicate that the photoexcitation of ZnP-D-C 60 in benzonitrile (PhCN) results in formation of the exciplex, which decays to the ground state without forming the charge-separated state. The strong interaction between the ZnP and the C 60 moieties due to the short linkage distance in ZnP-D-C 60 as indicated by the observation of the strongest CT band at the ground state results in formation of the exciplex. The energy of the exciplex is lower than that of the chargeseparated state even in a polar solvent such as PhCN. In contrast, the photoexcitation of the dyad with longer linkage, ZnP-O-C 60 , in PhCN results in formation of the charge-separated state via the exciplex formation, which is higher in energy than the charge-separated state. The photodynamics of exciplex formation of porphyrin-C 60 -linked dyads with a short linkage is characterized by the extremely fast formation rate from the singlet excited states of porphyrins involving both the second and first excited states due to the interaction between the porphyrin and C 60 moieties, which are placed at close proximity. In the case of MP-D-C 60 , the exciplex formation from the first singlet excited state of MP occurs at an ultrafast time scale with a time constant of 160 fs and that from the second singlet excited state occurs faster with a time constant less than 50 fs.

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Intramolecularly hydrogen-bonded organic compounds often exhibit fluorescence emission at considerably longer wavelengths than typical fluorescence as a result of excited-state intramolecular proton transfer (ESIPT). The structure-property relationship of such ESIPT molecules, however, remains obscure. The present article reports the excited-state dynamics of a new family of ESIPT molecules, 2-(2'-hydroxynaphthyl)benzazoles 1-3, based on steady-state and time-resolved spectroscopy measurements. In comparison with the parent compound HBO, all three compounds 1-3 exhibited absorption bands at longer wavelengths and emitted fluorescence from the excited keto-tautomer K* at shorter wavelengths, indicating that the introduction of a naphthalene ring increases the energy gap between the ground and excited states for the keto-tautomer despite the expansion of the aromatic ring. Time-resolved fluorescence spectra revealed dual emission for compounds 1 and 3, consisting of two distinct fluorescence bands originating from K* and the excited rotamer E'*, whereas 2 exhibited fluorescence only from the K* state. In the transient absorption spectra, both the T-T absorption band and the ground state absorption band of the Z-keto tautomer were observed for 1, whereas only the T-T absorption band was observed for 2 and only the Z-keto tautomer band was observed for 3.

Atomically flat, sputter-grown Au(111) films allowed well-ordered alkanethiol (exemplified by octanethiol) monolayers to be self-assembled from solution markedly faster and in larger domain sizes than previously reported. An X-ray photoelectron spectroscopy analysis showed that complete monolayer coverage was reached by 0.2−60 min of incubation in 0.1−0.001 mM ethanolic solution at room temperature (∼17 °C), with single-step (0.1 and 0.01 mM) or two-step (0.001 mM) adsorption kinetics. Increasing the temperature to 35 °C was enough to cause a single-step, diffusion-controlled adsorption also from the 0.001 mM solution, yielding the full monolayer coverage in approximately 10 min. Scanning tunneling microscopy (STM) imaging proved that well-ordered islands, with the (√3 × √3)R30° structure more-or-less strongly modulated by the c(4 × 2) superlattice, begin to form at 0.6−0.7 monolayer coverage most likely by homogeneous nucleation and grow rapidly thereafter. This kinetics of ordering requiring the considerably high threshold coverage for the nucleation, but allowing the fast growth of the nuclei was independently confirmed by the infrared reflection absorption spectroscopy. A typical c(4 × 2) domain size at the saturation coverage was estimated to be no less than 10−15 nm, and the structural identity often seemed not to be disrupted even across the etch pits. This superior structural order is reflected on the highest level of molecular resolution achieved by the in-air STM imaging. The expected registry of the (√3 × √3)R30° or c(4 × 2) lattice with that of Au(111) was also confirmed. On Au films that were also sputter-grown but no longer atomically flat, we observed at least by 1 order of magnitude slower self-assembly.

W h e n an aqueous AgCI0,-sodium dodecylsulphate (SDS)-isopropyl alcohol (Pr' OH) solution was photolysed with 253.7 nm light, a sharp and intense absorption band of colloidal silver (A = 390-400 nm) appeared after a relatively long induction period. In contrast, t h e sharp colloidal absorption rapidly developed when an AgCI0,-SDS-acetone [(CH,),CO] solution was irradiated under t h e s a m e conditions. It has been shown by chemical analysis and TEM characterization of t h e reduced silver that some of t h e colloidal silver agglomerates formed as a result of photolysis were peptized to fine silver particles during irradiation. Acetone ketyl radical formed by excitation of (CH3),C0 with 253.7 nm light seems to have an ability to peptize colloidal agglomerate in t h e solution phase (peptizing action). A novel ' photo-acetone method' available for preparation of fine metal particles has been proposed and applied to obtain colloidal gold, copper and platinum.We have studied photochemical formation of metal particles and thin films under fairly mild condition^.'-^ In a previous paper,, we reported that colloidal silver, gold and platinum are formed by irradiation of AgClO, , HAuCl, and Na,PtCl,

Colloidal silver and gold have been formed by irradiation of AgC10, and HAuC1, solutions with 253.7 nm light in the presence of protective agents such as sodium dodecylsulphate, sodium alginate and colloidal silica. Absorption maxima of colloidal silver and gold have been observed at 390-420 and 540-560 nm, respectively. Colloidal metals have been purified by dialysis and their amounts analysed quantitatively. The quantum yields of metal deposition are 0.053-0.15 for colloidal silver and 0.030-0.039 for colloidal gold. The quantum yield is increased several times by the use of protective agents, with the exception of a AgClO,-sodium alginate solution,

Systematic series of indium tin oxide (ITO) electrodes modified covalently with self-assembled monolayers (SAMs) of ferrocene-porphyrin-fullerene triads and porphyrin-fullerene dyads were designed to gain valuable insight into the development of molecular photovoltaic devices. The structures of SAMs on ITO have been investigated by UV/Vis absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The photoelectrochemical and photophysical (fluorescence lifetime and time-resolved transient absorption) properties were also determined. The highest quantum yield of photocurrent generation (11 %) among donor-acceptor linked systems which are covalently attached to the surface of ITO electrodes was achieved with SAMs of ferrocene-zinc porphyrin-fullerene linked triad on ITO electrodes. The quantum yields of photocurrent generation correlate well with the charge-separation efficiency and the lifetime of the charge-separated state of the porphyrin-fullerene linked systems in solution. These results provide valuable information for the construction of photonic molecular devices and artificial photosynthetic systems on ITO electrodes.

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