Halogen-bridged Platinum Complexes Research Articles

23aN-7 擬一次元ハロゲン架橋白金錯体中の局在励起子における振動緩和過程

23aN-7 擬一次元ハロゲン架橋白金錯体中の局在励起子における振動緩和過程

Excitation photon energy dependence of the relaxation processes of the photoexcited states in a quasi-one-dimensional halogen bridged Pt complex

Excitation photon energy dependence of the relaxation processes of the photoexcited states in a quasi-one-dimensional halogenbridged platinum complex has been investigated by femto second transient absorption measurements. In a Pt complex, [Pt(en)2][Pt(en)2I2](SO4)2.6H2O (Pt-I-SO4), a photo-induced absorption (PA) band caused by self trapped excitons (STE’s) has been observed when the excitation photon energy is close to the peak energy, 1.44 eV, of the absorption band of the one photon allowed charge transfer (CT) exciton with odd parity. In addition, a long lived PA bands caused by charged solitons (CS’s) has been observed. The intensity of these long lived CS absorption band shows quadratic excitation power dependence. This shows that CS’s pairs are not generated from odd-CT-excitons but from the higher energy two photon excited states. When the excitation photon energy is close to a half of the of the even CT- exciton energy, 1.84 eV, PA bands caused by STE’s and CS’s have been observed. These states are generated from the two photon excited even CT-excitons. When the excitation photon energy is much higher than the energy of the odd CT-exciton, PA bands caused by CS’s and polarons have been observed. The intensities of these PA bands show linear excitation power dependences. Photo-generated free electron hole pairs are considered to relax into CS’s and polarons.

Splitting dynamics of nuclear wave packets in a Peierls insulator using femtosecond laser spectroscopy

We investigated the wave-packet (WP) dynamics corresponding to the lattice rearrangement in halogen-bridged platinum complex with femtosecond luminescence spectroscopy. We revealed a motion of the splitting process of WP at the top of a potential barrier on the adiabatic potential-energy surface connecting the self-trapped exciton and the soliton-pair state. By changing the kinetic energy of the WP, we succeeded in controlling the propagation efficiency of WP beyond the barrier by a factor of 250%. The anomalous dwelling behavior and quantum interference of the WP were also observed. The obtained envelope of the WP clarified the dynamical process of the splitting and interfering time-dependent wave functions, providing a picture of lattice rearrangement in terms of quantum-mechanical waves.

Wavepacket Motion in Self-Trapped Exciton of Quasi-One-Dimensional Halogen-Bridged Pt Complex, [Pt(en)2][Pt(en)2I2] (ClO4)4, Observed by Femtosecond Time Resolved Luminescence Spectroscopy

We report on the time-resolved luminescence spectroscopy of a quasi-one-dimensional halogen-bridged platinum complex, [Pt(en) 2 ][Pt(en) 2 I 2 ] (ClO 4 ) 4 , at room temperature in the energy range between 1.2 and 0.9 eV. A strong first peak at the time origin and subsequent oscillating features were observed in the time evolution curves of luminescence intensity. As the frequency of the wavepacket oscillation in the self-trapped exciton, we obtained 2.92 THz (97 cm -1 ), which is 77% of the symmetric stretching mode frequency in the ground state. We analyzed the measured time evolution of the luminescence intensity by using the theory of resonant secondary radiation.

Optical observations of new halogen-bridged platinum complexes assembled within a ladder lattice

New varieties of quasi-one-dimensional transition metal (M)-halide (X) compounds, $$(\hbox{C}_8\hbox{H}_6\hbox{N}_4)[\hbox{Pt}(\hbox{C}_2\hbox{H}_8\hbox{N}_2)\hbox{Cl}]_2\hbox{Cl}(\hbox{ClO}_4)_3\cdot \hbox{H}_2\hbox{O}$$ and $$(\hbox{C}_{10}\hbox{H}_8\hbox{N}_2)[\hbox{Pt}(\hbox{C}_4\hbox{H}_{13}\hbox{N}_3)\hbox{Br}]_2\hbox{Br}_4\cdot 2\hbox{H}_2\hbox{O},$$ comprising two-leg ladders of mixed-valent platinum complexes, are theoretically investigated with particular emphasis on their photoresponses. Observations of the polarized optical conductivity prove the interchain valence arrangement to be in phase in the former but out of phase in the latter. Possible nonlinear lattice relaxation originating with a photogenerated exciton is also simulated in an attempt to further elucidate the contrast between them.

Density Functional Theory of Chlorine-Bridged Platinum Complexes: Monomer, Chain, and Two-Leg Ladders

Novel halogen-bridged platinum complexes, namely, their two-leg ladder versions, have been synthesized for the first time and their basic properties including optical spectra are now available. Motivated by this progress, we investigate chlorine-bridged systems by density-functional-theory calculations. Our scope is over various geometrical types such as a monomer, a single chain, and ladders. We treat not only ground states but also excited states, calculating optical conductivity spectra, which show features specific to the ladder systems. As a result of a comparison with the experimental spectra, an overall agreement is at least qualitatively attained and a new mechanism of hole photo-doping is proposed.

Self-Assembled Nanowires of Lipid-packaged Halogen-bridged Platinum Complexes Formed by One-pot Oxidation of Pt(en)2 complexes by Au(III) Ions

Abstract A solution-phase synthesis of lipid-packaged mixed valence platinum complexes is newly developed. Addition of aqueous HAuCl4 or AuBr3 to Pt(en)2[1]2 complex dissolved in dichloromethane affords halogen-bridged linear complexes [Pt(en)2][Pt(en)2X2][1]4 (X = Cl or Br). Formation of self-assembled nanowires was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy.

Nuclear wave-packet dynamics in the localized excitons of halogen-bridged platinum complexes

The luminescence of self-trapped excitons in halogen-bridged platinum complexes [Pt(en) 2] [Pt(en) 2X 2](ClO 4) 4 (en=ethylenediamine, X=Br, Cl) has been studied by means of femtosecond up-conversion techniques. The time evolution of the nuclear wave-packet shape is visualized for a Pt–Br system and interpreted in terms of a harmonic-oscillator model.

Ultrafast Lattice Relaxation Phenomena Studied by Time-Resolved Luminescence Spectroscopy

Recent developments in the ultrafast luminescence spectroscopy are reviewed. Principles of time-resolved luminescence measurements i.e., the optical Kerr shutter method and the up-conversion technique are described. The formation and relaxation processes of self-trapped excitons in quasi-one-dimensional halogenbridged platinum complexes (Pt-Cl, Pt-Br, Pt-I) are studied by luminescence up-conversion technique. The lifetime of the self-trapped excitons shows a systematic decrease as the mass of the halogen ion increases, showing the increased probability of non-radiative decay processes. The real-time capturing of the nuclear wave-packet form is successfully demonstrated in Pt-Br and good agreements with calculation are obtained. The luminescence in the picosecond region has been observed in the halogen-bridged nickel complex, and a coexistence of localized excitons with small and large lattice relaxations is suggested.

Real-time capturing of the nuclear wave-packet shape in self-trapped excitons.

We measured the time evolutions of the luminescence spectra in a quasi-1D halogen-bridged platinum complex [Pt(en)(2)][Pt(en)(2)Br(2)](ClO4)(4) with a 50 fs resolution up-conversion spectroscopy and succeeded in real-time visualization of the shape of the wave packet (WP) propagating on the adiabatic potential surface of a self-trapped exciton. The behavior of the WP is in excellent agreement with a calculation based on a harmonic oscillator. We have found that the damping of the WP oscillation is highly nonexponential.

OVERTONE MODULATION AND ANTI-PHASING BEHAVIOR OF WAVE-PACKET AMPLITUDES ON THE ADIABATIC POTENTIAL SURFACE OF SELF-TRAPPED EXCITONS

The detailed behavior of the wave-packet motion on the adiabatic potential surface of a self-trapped exciton is investigated in the quasi-one-dimensional halogen-bridged platinum complex [Pt(en) 2 ][Pt(en) 2 Br 2 ](ClO 4 ) 4 by means of time resolved luminescence spectroscopy. We have achieved a time-resolution of about 40 fs and found the frequency of the luminescence intensity oscillation twice as high as that of the wave-packet oscillation. Furthermore we have confirmed the anti-phasing behavior between the luminescence oscillations on the opposite sides of the potential minimum. Analyzing these results, we have succeeded in tracing the center of gravity motion of the wave-packet on the femtosecond time scale.

Ultrafast dynamics of lattice relaxation of excitons in quasi-one-dimensional halogen-bridged platinum complexes

The temporal evolution of the photoexcited state in quasi-one-dimensional (1D) halogen-bridged platinum complexes $[\mathrm{Pt}(\mathrm{en}{)}_{2}][\mathrm{Pt}(\mathrm{en}{)}_{2}{X}_{2}]({\mathrm{ClO}}_{4}{)}_{4}$ (abbreviated as $\mathrm{Pt}\ensuremath{-}X,$ $X=\mathrm{C}\mathrm{l},$ Br or I), has been comprehensively studied by femtosecond time-resolved luminescence spectroscopy. In Pt-Cl, new short-lived hot luminescence is found in the low-energy side of a self-trapped exciton (STE) luminescence band. The overall behavior of the STE luminescence band within 2 ps is well explained by the vibrational relaxation of the STE. The behavior is reproduced by a model calculation based on wave packet propagation on an interaction mode composed of frequency-dispersed bulk phonons. This model is also applied to the previous results in Pt-Br. For both Pt-Cl and Pt-Br, the frequency spectra of phonons which compose the interaction mode have been estimated. In Pt-I, the STE luminescence decays much faster than those in Pt-Cl and Pt-Br, showing existence of more effective nonradiative decay channel.

Relaxation Dynamics In Photo-Excited Halogen-Bridged Pt-Complexes Studied By Femtosecond Luminescence Spectroscopy

The ultrafast dynamics of excited electronic states in a series of quasi-one-dimensional halogen-bridged platinum-complexes was investigated by using femtosecond luminescence spectroscopy. In Pt-Br system, the wave-packet oscillation of the local vibration of self-trapped excitons (STEs) was observed. The time evolutions of luminescence intensity in Pt-Br and Pt-Cl were successfully described by using a model based on a wave-packet motion on the interaction mode coordinate. In Pt-I, very fast decay was observed, suggesting the existence of efficient non-radiative decay channel directing to structural change.

Mixed-Valence State of a One-Dimensional Platinum Complex with a Counter Ion Having Two Alkyl Chains and its Liquid Crystal Phase

We have investigated optical property and crystal structure of a one-dimensional halogen-bridged platinum complex (MX chain compound) with a counter ion having two alkyl chains, [Pt(en) 2 ][PtCl 2 (en) 2 ]{(CH 3 (CH 2 ) 7 CO 2 ) 2 CH 2 CHSO 3 } 4 2H 2 O, to elucidate influence of molecular fastener effect of the long alkyl chain on mixed-valence state of the platinum atoms. Thermal-behavior observations of the complex were also performed using a polarizing optical microscope without and with crossed nicols to examine thermal change of the mixed-valence state and appearance of the liquid crystal phase. Consequently, the complex has exhibited that the interaction between the platinum atoms is strengthened and the Pt II -Pt IV distance is shortened by doubling the number of alkyl chains around the platinum complex moieties compared with a corresponding PtCl chain complex with a single alkyl chain counter ion. We have also observed a texture of liquid crystal at about 200C. Mixed-Valence State One-Dimensional Halogen-Bridged Platinum Complex Long Alkyl Chain Molecular Fastener Effect Liquid Crystal Phase

BRIDGING-HALOGEN DEPENDENCE OF ULTRAFAST DYNAMICS OF EXCITONS IN QUASI-ONE-DIMENSIONAL PLATINUM COMPLEXES

The femtosecond time-resolved luminescence of a quasi-one-dimensional halogen-bridged platinum complex [ Pt(en) 2][ Pt(en) 2 I 2] (CIO4)4 (abbreviated as Pt-I) is observed. The observed lifetime of the exciton luminescence is rather shorter than those of the other Pt-X (X = halogen ion) systems which have relatively wider band gaps. This result is considered to show that the nonradiative relaxation process becomes more efficient in the narrow-gap system Pt-I.

Femtosecond relaxation dynamics of excitons in 1D CDW systems

The temporal behavior of the luminescence from self-trapped excitons has been investigated in quasi-one-dimensional halogen-bridged platinum complexes, Pt–Cl, Pt–Br and Pt–I, which have the charge density wave (CDW) state as their ground states. The experimental results are comprehensively understood in terms of a theoretical model of the wave-packet oscillation on the interaction mode considering the dephasing process. The systematic decrease of the lifetime of STE with increasing the mass of the halogen ions suggested increased probability of non-radiative decay channel toward the rearranged CDW ground state starting from the exciton localization.

Self-assembling molecular wires of halogen-bridged platinum complexes in organic media. Mesoscopic supramolecular assemblies consisting of a mixed valent Pt(II)/Pt(IV) complex and anionic amphiphiles.

A novel class of supramolecular assemblies in organic media consisting of a molecular wire of a halogen-bridged platinum complex [Pt(en)2][PtCl2(en)2]4+ (en = 1,2-diaminoethane) and anionic amphiphiles is developed. When double-chained phosphates or sulfonates are employed, the resultant [Pt(en)2][PtCl2(en)2](4+)-lipid complexes displayed intervalence charge transfer (CT) absorption bands in the crystalline state. They are soluble in organic solvents because of the amphiphilic superstructure, in which the solvophobic one-dimensional platinum complex is surrounded by solvophilic alkyl chains. CT absorption bands of halogen-bridged linear complexes are maintained in organic media, with varied colors that depend on the chemical structure of constituent amphiphiles. Monoalkylated phosphates failed to form colored, halogen-bridged ternary complexes probably because of their coordination to the axial position of PtII(en)2. Formation of mesoscopic supramolecular assemblies in organic media was confirmed for the [Pt(en)2][PtCl2(en)2] complexes by electron microscopy. Interestingly, a supramolecular complex consisting of dihexadecyl sulfosuccinate and [Pt(en)2][PtCl2(en)2]4+ displayed clear, indigo solutions that are distinct from the yellow color observed for those of [Pt(en)2][PtCl2(en)2]/dialkyl phosphate complexes. The indigo color of the former complex disappeared upon heating the solution to 60 degrees C, whereas it reappeared reversibly by cooling the solution to room temperature. In electron microscopy, rodlike nanostructures with a minimum width of 18 nm and lengths of 700-1700 nm were observed after cooling, though not at elevated temperatures. Apparently, the lipid-[Pt(en)2][PtCl2(en)2]4+ complex undergoes reversible dissociation and reassembly processes in chloroform, and it becomes better dispersed after the reassembling process. The present finding opens a general route to solution chemistry of low-dimensional inorganic complexes and enables rational design and control of self-assembling inorganic molecular wires.

Organization of One-Dimensional Mixed-Valence Platinum Complexes at the Air-Water Interface and in Langmuir-Blodgett Films

Surface monolayers consisting of cationic, halogen-bridged linear platinum complex and anionic amphiphiles are formed at the air-water interface. Lipophilic polyion complex prepared from lipid and one-dimensional platinum complex is dispersed in chloroform as an indigo-colored solution, which color is ascribed to charge transfer (CT) absorption of the halogen-bridged complex (PtII→PtIV). Upon heating the solution, the indigo color disappeared due to dissociation of the linear complex into molecular unit complexes. Oriented surface monolayer is formed on water by spreading the colorless chloroform solution. Appearance of the CT band in reflectance spectra of monolayers indicates that the one-dimensional halogen-bridged complex is reformed at the air-water interface. The present technique opens an avenue to dimension-controlled organization of linear halogen-bridged complexes.

Observation of the wave-packet oscillation during the exciton self-trapping process in a quasi-one-dimensional halogen-bridged Pt complex

Using femtosecond time-resolved luminescence spectroscopy, we have observed a wave-packet oscillation in an adiabatic potential well associated with a self-trapped exciton (STE). We have investigated the STE luminescence band of a quasi-one-dimensional halogen-bridged platinum complex $[{\mathrm{Pt}(\mathrm{en})}_{2}][{\mathrm{Pt}(\mathrm{en})}_{2}{\mathrm{Br}}_{2}]({\mathrm{ClO}}_{4}{)}_{4}.$ In the time evolution of the luminescence, we have observed an oscillation with a period of about 300 fs. This result shows the formation of a wave packet and its oscillation, which is damped with the time constant of about 430 fs. The STE's have a lifetime of about 5.5 ps at room temperature.

Femtosecond Dynamics of the Exciton Self-Trapping Process in a Quasi-One-Dimensional Halogen-Bridged Platinum Complex

Self-trapped-exciton (STE) luminescence of quasi-one-dimensional halogen-bridged platinum complex $[\mathrm{Pt}(\mathrm{en}{)}_{2}][\mathrm{Pt}(\mathrm{en}{)}_{2}{\mathrm{Cl}}_{2}]({\mathrm{ClO}}_{4}{)}_{4}$ is investigated by femtosecond time-resolved luminescence spectroscopy. In the high energy tail of the luminescence band, a fast rise and decay are seen, whereas around the luminescence peak energy a slow rise of about 500 fs is observed. This rise becomes faster at the low energy side of the band. These results are consistently explained by the cooling of prethermalized STEs, following the rapid self-trapping which is estimated to occur within 140 fs.