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. Vibrational relaxation in the potential surface of the proton transferred tautomer of alizarin and the population decay occurring with two distinct time scales were also observed in addition to the solvation dynamics of DMSO solvent molecules.

Particle-size-dependent fluorescence enhancements and dynamics on homogeneous silver nanosurfaces show a strong dependence on the spectral properties of surface plasmons.

The excited state Raman spectra of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-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. On the other hand, the energy of the ICT state of DCM becomes higher than that of the LE state in a less polar chloroform solution, where the initially-photoexcited ICT state with the LE state shows the ultrafast internal conversion to the LE state with a time constant of 300 fs. The excited-state Raman spectra of the LE and ICT state of DCM showed several major vibrational modes of DCM in the LE and ICT conformer states coexisting in the excited state. Comparing to the time-dependent density functional theory simulations and the experimental results of similar push-pull type molecules, a twisted geometry of the dimethylamino group is suggested for the structure of DCM in the S1/ICT state.

The fluorescence of dye molecules often shows a strong increase in intensity near metal surfaces or nanoparticles. The excited-state dynamics of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) in the presence of a silver island film (SIF) were explored by femtosecond transient absorption spectroscopy. Under 403 nm excitation, we found clear differences in the excited-state spectra and kinetics of DCM with the SIF. From the analysis of the emission kinetics of DCM, an additional process with a 40−60 ps time constant was distinguished, which was hypothesized to be surface plasmon-coupled fluorescence. This ultrafast process for 403 nm excitation was confirmed as ultrafast energy transfer directly from the surface plasmon of the SIF to DCM. Under 480 nm excitation, no such ultrafast process was observed, but a constant increase in the emission intensity by ∼10% due to the increased electric field of the silver nanoparticles occurred.