摘要:

A new model of hierarchical structure in J-aggregates,mesoaggregatesandmacroaggregates, is proposed on the basis of the linear and nonlinear optical properties of the oriented J-aggregates prepared by a novel vertical spin-coating method. The concentration dependence of dichroic spectra, wavelength dependence of hole-burning efficiency, and polarization dependence of electroabsorption are studied. The mesoaggregate is characterized by coherent exciton delocalized over the mesoscopic size, while the macroaggregate can be oriented by macroscopic centrifugal force of solvent flow. The macroaggrcgale is constituted by an incoherent ensemble of the mesoaggregates alternately stacked.

ISSN:1058-725X    

DOI:10.1080/10587259808042451

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A method determining the exciton bandwidth in aromatic microcrystallites is presented, and the behavior of Frenkel excitons in these substances is reviewed. The spectral bandwidth of excitation spectra of luminescence from microcrystallites is found to increase linearly with the microcrystallite size in anthracene and superlinearly in pyrene. A strong exciton scattering component at microcrystallite surfaces is found in anthracene microcrystallites. The k selection rule that is lost in small microcrystallites is recovered for large microcrystallites at a size of 134 Å in anthracene and 50 Å in pyrene. With these values, the surface scattering layer thickness is estimated to be 32 Å in anthracene, but nearly zero in pyrene microcrystallites. We suggest that the concept of the exciton migration in microcrystallites can be applied to biological systems where only 5 ∼ 10 molecules are arranged.

ISSN:1058-725X    

DOI:10.1080/10587259808042452

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The “nanoshock technique” for generating shock waves in molecular materials at high repetition rates is described. Ultrafast spectroscopy is used to study shock waves in crystalline anthracene, a high explosive NTO, and a molecular nanomachine, the heme protein myoglobin.

ISSN:1058-725X    

DOI:10.1080/10587259808042453

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Experimental and theoretical evidence is presented for the process of directed, multistep energy transport in a unique class of fractal-like dendrimeric supermolecules. Due to the meta-position branching arrangement of these Cayley trees, tight excitation localization is observed at the branching nodes. Particular forms of these dendrimers have been synthesized with localized states of decreasing energy toward the molecular locus, creating a rapid and efficient exciton funnel. Spectroscppic data is presented illustrating nearly unit transfer efficiency from the dendrimer periphery to a specialized trap at the molecular center. In addition, the energetics and spatial arrangement of these molecules allow for the destruction of multiphoton excitations at the trap, providing protection from permanent photochemical bleaching.

ISSN:1058-725X    

DOI:10.1080/10587259808042454

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The electronic excitation on the surface of rare gas solids can lead the desorption of a variety of species. Close investigation of the desorption phenomena will reveal the dynamical aspect of the electronic excitation and its relaxation process at the surface. In the case of rare gas solids, the desorption of an excited neutral particle is closely related to the production of an exciton.

ISSN:1058-725X    

DOI:10.1080/10587259808042455

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Relaxation dynamics of photoexcited stales in ultrathin multilayered films composed of copper phthalocyanine (CuPc) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), were investigated by femtosecond absorption spectroscopy. Absorption bands due to an electronically excited state and a vibrationally excited state of electronically ground state of CuPc were measured for the excitation at 390 nm and 780 nm. Furthermore, an additional absorption band was observed when excited at 390 nm, which was assigned to an NTCDA excited state. Ultrafast energy transfer from NTCDA to CuPc takes place with the time scale of 1 ps at the interface between NTCDA and CuPc layers.

ISSN:1058-725X    

DOI:10.1080/10587259808042456

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Temperature dependence of the relaxation processes from the photo-excited state in Platinum dimethylglyoxime complex (Pt(dmg)2) film was investigated by femtosecond pump- probe spectroscopy. Measurements were made at 300K and 80K. The exciton lifetime estimated from the decay of the excited state absorption was 21ps at both temperatures. This suggests that the thermal barrier associated with the relaxation to the ground state is very small. The intensity of bleaching of exciton absorption caused by third order nonlinear susceptibility was about ten times larger at 80K than at 300K. It suggests that an excited state with higher electronic coherence exists at lower temperatures. An ultrafast bleaching component decaying within 400fs which is observed only at 80K is considered to arise from the the electronic coherence of the excited state.

ISSN:1058-725X    

DOI:10.1080/10587259808042457

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A silicon phthalocyanine (Pc) compound PcSi[OSi(CH3)3]2in solid phase emitted a relatively intense fluorescence as compared with other solid Pc compounds. At room temperature fluorescence spectrum of the solid SiPc had three major bands peaking at 715, 781 and 840 nm, and total fluorescence yield was estimated to be ∼10−2, which was about 1/20 of that of solution. Different time-resolved decay profiles of these bands proved that the fluorescence had at least two emission origins. With decreasing temperature fluorescence intensity and spectrum changed drastically. In particular, below 60 K the 715 nm band became quite sharp and intense. Total intensity at 5 K was about ten times as large as that at 300 K.

ISSN:1058-725X    

DOI:10.1080/10587259808042458

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Photoinduced absorption from singlet excited states in conjugated polymers are theoretically studied by a Pariser-Parr-Pople type model. Full valence-bond calculations indicate that, when the two possible lowest singlet excited states (the so-called 2Agand 1Busates) are nearly degenerate, absorption from them are quite similar in their spectral features, in spite of much different characters of these two states.

ISSN:1058-725X    

DOI:10.1080/10587259808042459

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Fluorescence properties of azobenzene liquid crystal, 4,4′-dioctyloxy- azobenzene, were examined by steady-state and picosecond single-photon timing spectroscopy. It was found that the fluorescence from azobenzene aggregate with a peak at ∼ 630 nm was observed in the solid phase in addition to the very weak S2fluorescence from azobenzene monomer centered at 420 nm. The fluorescence lifetimes of both aggregate and monomer S2state were estimated to be approximately 150 ps and shorter than 2 ps. The relationship between the excited-state dynamics of azobenzene liquid crystal and its phase transition was analyzed on the basis of the temperature dependence of relative fluorescence intensity and fluorescence lifetime of aggregate.

ISSN:1058-725X    

DOI:10.1080/10587259808042460

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor