Site-Specific Photochemistry along a Protonated Peptide Scaffold.

We present a detailed study of the time-dependent photophysics and photochemistry of a known conformation of the two protonated pentapeptides Leu-enkephalin (Tyrosine-Glycine-Glycine-Phenylalanine-Leucine, YGGFL) and its chromophore-swapped analogue FGGYL, carried out under cryo-cooled conditions in the gas phase. Using ultraviolet-infrared (UV-IR) double resonance, we record excited state IR spectra as a function of time delay between UV and IR pulses. We identify unique Tyr OH stretch transitions due to the S state and the vibrationally excited triplet state(s) formed by intersystem crossing, T(v).

Capturing CO in Quadrupolar Binding Pockets: Broadband Microwave Spectroscopy of Pyrimidine-(CO), = 1,2.

Pyrimidine has two in-plane CH(δ+)/(δ-)/CH(δ+) binding sites that are complementary to the (δ-/2δ+/δ-) quadrupole moment of CO. We recorded broadband microwave spectra over the 7.5-17.

Molecular Cage Reports on Its Contents: Spectroscopic Signatures of Cryo-Cooled K- and Ba-Benzocryptand Complexes.

UV photofragment spectroscopy and IR-UV double resonance methods are used to determine the structure and spectroscopic responses of a three-dimensional [2.2.2]-benzocryptand cage to the incorporation of a single K or Ba imbedded inside it (labeled as K-BzCrypt, Ba-BzCrypt).

Jet-Cooled Phosphorescence Excitation Spectrum of the T(n,π*) ← S Transition of 4-Pyran-4-one.

The 4-pyran-4-one (4PN) molecule is a cyclic conjugated enone with spectroscopically accessible singlet and triplet (n,π*)excited states. Vibronic spectra of 4PN provide a stringent test of electronic-structure calculations, through comparison of predicted vs measured vibrational frequencies in the excited state. We report here the T(n,π*) ← S phosphorescence excitation spectrum of 4PN, recorded under the cooling conditions of a supersonic free-jet expansion.