Twisted intramolecular charge transfer of nitroaromatic push-pull chromophores.

The structural changes during the intramolecular charge transfer (ICT) of nitroaromatic chromophores, 4-dimethylamino-4'-nitrobiphenyl (DNBP) and 4-dimethylamino-4'-nitrostilbene (DNS) were investigated by femtosecond stimulated Raman spectroscopy (FSRS) with both high spectral and temporal resolutions. The kinetically resolved Raman spectra of DNBP and DNS in the locally-excited and charge-transferred states of the S state appear distinct, especially in the skeletal vibrational modes of biphenyl and stilbene including ν and ν. The ν of two phenyls and the ν of the central ethylene group (only for stilbene), which are strongly coupled in the planar geometries, are broken with the twist of nitrophenyl group with the ICT.

Intramolecular charge transfer of a push-pull chromophore with restricted internal rotation of an electron donor.

Intramolecular charge transfer (ICT) of 4-(dicyanomethylene)-2-methyl-6-[2-(2,3,6,7-tetrahydro-1,5-benzo[]quinolizin-9-yl)vinyl]-4-pyran (LD688) in DMSO solution was investigated by femtosecond stimulated Raman spectroscopy (FSRS) with 403 nm excitation. The molecular structure of LD688 is similar to that of a well-known push-pull chromophore, 4-dicyanomethylene-2-methyl-6-(-dimethylaminostyryl)-4-pyran (DCM), except that the internal rotation of the electron-donating dimethylamino group is restricted with the introduction of the julolidine moiety. Upon photo-excitation, LD688 shows an ultrafast (1.

Intramolecular Charge Transfer of Curcumin and Solvation Dynamics of DMSO Probed by Time-Resolved Raman Spectroscopy.

Intramolecular charge transfer (ICT) of curcumin in dimethyl sulfoxide (DMSO) solution in the excited state was investigated by femtosecond electronic and vibrational spectroscopy. Excited-state Raman spectra of curcumin in the locally-excited and charge-transferred (CT) state of the S excited state were separated due to high temporal (<50 fs) and spectral (<10 cm) resolutions of femtosecond stimulated Raman spectroscopy. The ultrafast (0.

Intramolecular Charge Transfer of 1-Aminoanthraquinone and Ultrafast Solvation Dynamics of Dimethylsulfoxide.

The intramolecular charge transfer (ICT) of 1-aminoanthraquinone (AAQ) in the excited state strongly depends on its solvent properties, and the twisted geometry of its amino group has been recommended for the twisted ICT (TICT) state by recent theoretical works. We report the transient Raman spectra of AAQ in a dimethylsulfoxide (DMSO) solution by femtosecond stimulated Raman spectroscopy to provide clear experimental evidence for the TICT state of AAQ. The ultrafast (~110 fs) TICT dynamics of AAQ were observed from the major vibrational modes of AAQ including the ν + δ and ν modes.

Twisted Intramolecular Charge Transfer State of a "Push-Pull" Emitter.

The excited state Raman spectra of 4-dicyanomethylene-2-methyl-6-(-dimethylaminostyryl)-4-pyran (DCM) in the locally-excited (LE) and the intramolecular charge transfer (ICT) states have been separately measured by time-resolved stimulated Raman spectroscopy. In a polar dimethylsulfoxide solution, the ultrafast ICT of DCM with a time constant of 1.0 ps was observed in addition to the vibrational relaxation in the ICT state of 4-7 ps.

Ultrafast intramolecular proton transfer reactions and solvation dynamics of DMSO.

Ultrafast intramolecular proton transfers of 1,2-dihydroxyanthraquinone (alizarin-h) and its deuterated product (alizarin-d) in dimethyl sulfoxide (DMSO) have been investigated by femtosecond stimulated Raman spectroscopy. The population dynamics in the solute vibrational mode of ν and the coherent oscillations observed in all of the skeletal vibrational modes ν and ν clearly showed the ultrafast excited-state intramolecular proton transfer dynamics of 110 and 170 fs for alizarin-h and alizarin-d, respectively. Interestingly, we have observed that the solvent vibrational modes ν and ν may also represent ultrafast structural dynamics at the frequencies for its "free" or "aggregated" species.

Homogeneous silver colloidal substrates optimal for metal-enhanced fluorescence.

Homogeneous silver colloidal films (SCFs), composed of silver nanoparticles 67-193 nm in diameter, were synthesized by a seeded-growth method as the substrates for metal-enhanced fluorescence (MEF). The homogeneity and uniform particle distribution of the SCFs showed many advantages for the exploration of the MEF mechanism. The fluorescence enhancement of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) and rhodamine 700 (Rh700) dyes dispersed in a thin layer of polystyrene (PS) with the SCFs was observed by time-resolved fluorescence spectroscopy.

Ultrafast Intramolecular Proton Transfer of Alizarin Investigated by Femtosecond Stimulated Raman Spectroscopy.

We report time-resolved stimulated Raman spectra of alizarin in DMSO solution with 403 nm excitation. Upon photoexcitation, the intramolecular proton transfer reaction of alizarin occurs in 70-80 fs, which is confirmed by both the population growth and the frequency and bandwidth changes of skeletal vibrational modes of alizarin. Interestingly, the vibrational frequencies of ν(C═C) and ν(C═O) show opposite shifts during the reaction, which may implicate changes in the resonance structure of anthraquinone and the attached carbonyl group.