A recent density functional perturbation theory calculation of the vibrational frequencies of C60 is compared with the infrared spectrum of the crystal. The vibrational assignment of C60 is completed with the help of the calculation plus the available infrared, Raman, and inelastic neutron scattering spectra.

Surface-enhanced Raman scattering (SERS) of adenine-containing microRNA chains has been obtained by adsorption on roughened silver substrates. The spectral features of all of these samples appear dominated by the bands of adenine. By comparison with the SERS spectra of adenine and adenosine obtained on the same substrates, along with DFT calculations on the interaction sites of adenine and adenosine with silver, inferences are discussed about the structural arrangement of the microRNA chains with respect to the metal surface. This approach gives suitable guidelines in order to investigate the adsorption of complex biomolecules on metal substrates.

The infrared and Raman spectra of all-trans-retinal in the region of the low-frequency internal vibrations have been measured at room temeprature and at 15 K. The frequencies and infrared intensities of the normal modes have been calculated by means of the density functional approach using the B3-LYP exchange + correlation functional. The vibrational analysis allows a complete assignment of all the observed fundamentals, both on a frequency and on a intensity basis. The calculated vibrational modes of all-trans-retinal have been also correlated to those of the component moieties, 3,7-dimethyl-2,4,6,8-octatetraenal and 1,3,3-trimethylcyclohexene. This gives an idea of the degree of localization of the vibrational modes. It turns out that many of them are localized on the ring or on the chain fragment of the molecule. The chain torsional modes, which are of primary interest for the photoisomerization process, are correlated with torsional modes of bacteriorhodopsin.

Fluorescence, S1 → S0, and fluorescence excitation, S0 → S1, spectra of 1,6-methano[10]annulene have been measured in glassy matrixes at low temperature under moderate site selection conditions. The polarization ratios of both spectra have been also measured at 77 K. MO ab initio calculations including correlation effects indicate that the molecule has one energy minimum in the ground state and one in the lowest excited singlet state. They correspond to bond-equalized structures of aromatic character. The spectra are accordingly discussed in terms of transitions involving the aromatic form of 1,6-methano[10]annulene. A good correlation is found between observed and calculated Franck−Condon intensities.

The relaxation dynamics of unsubstituted porphyrin (H2P), diprotonated porphyrin (H4P2+), and tetraoxaporphyrin dication (TOxP2+) has been investigated in the femtosecond-nanosecond time domain upon photoexcitation in the Soret band with pulses of femtosecond duration. By probing with spectrally broad femtosecond pulses, we have observed transient absorption spectra at delay times up to 1.5 ns. The kinetic profiles corresponding with the band maxima due to excited-state absorption have been determined for the three species. Four components of the relaxation process are distinguished for H2P: the unresolvably short B --> Qy internal conversion is followed by the Qy --> Qx process, vibrational relaxation, and thermalization in the Qx state with time constant approximately 150 fs, 1.8 ps, and 24.9 ps, respectively. Going from H2P to TOxP2+, two processes are resolved, i.e., B --> Q internal conversion and thermal equilibration in the Q state. The B --> Q time constant has been determined to be 25 ps. The large difference with respect to the B --> Qy time constant of H2P has been related to the increased energy gap between the coupled states, 9370 cm-1 in TOxP2+ vs 6100 cm-1 in H2P. The relaxation dynamics of H4P2+ has a first ultrafast component of approximately 300 fs assigned as internal conversion between the B (or Soret) state and charge-transfer (CT) states of the H4P2+ complex with two trifluoroacetate counterions. This process is followed by internal CT --> Q conversion (time constant 9 ps) and thermalization in the Q state (time constant 22 ps).