Janus-Type ESIPT Chromophores with Distinctive Intramolecular Hydrogen-bonding Selectivity.

Excited-state intramolecular proton transfer (ESIPT)-based solid luminescent materials with multiple hydrogen bond acceptors (HBAs) remain unexplored. Herein, we introduced a family of Janus-type ESIPT chromophores featuring distinctive hydrogen bond (H-bond) selectivity between competitive HBAs in a single molecule. Our investigations showed that the central hydroxyl group preferentially forms intramolecular H-bonds with imines in imine-modified 2-hydroxyphenyl benzothiazole (HBT) chromophores but tethers the benzothiazole moiety in hydrazone-modified HBT chromophores. Imine-derived HBTs generally exhibit higher fluorescence efficiency, while hydrazone-derived HBTs show a reduced overlap between the absorption and fluorescence bands. Quantum chemical calculations unveiled the molecular origins of the biased intramolecular H-bonds and their impact on the ESIPT process. This Janus-type ESIPT chromophore skeleton provides new opportunities for the design of solid luminescent materials.

Doppler-free/Doppler-sliced ion imaging.

We demonstrate a hybrid Doppler-free/Doppler-sliced ion imaging approach that is well-suited for detection of H or D atoms. The method relies on 2 + 1 resonant ionization with identical, nearly counterpropagating beams that are coplanar but directed at a small angle relative to the detector face. This results in Doppler selection of the velocity component along the time of flight axis but Doppler-free detection in the plane perpendicular to this axis. The results show high signal level and excellent slicing ( approximately 5%), yielding velocity resolution completely determined by cation recoil in the ionization step.

Photoelectron imaging of propanal by resonant multiphoton ionization via the 3s Rydberg state.

We report the conformationally- and vibrationally-selected photoelectron spectroscopy of propanal obtained by resonance-enhanced multiphoton ionization (REMPI) using photoelectron imaging. These photoelectron spectra, employing (2 + 1) ionization via the (n, 3s) Rydberg transitions in the range from 365 to 371 nm, confirm that there are two stable conformer origins in the lowest ionic state, the cis conformer with a co-planar CCCO geometry and a gauche conformer with a approximately 119 degrees CCCO dihedral angle. From ab initio calculations at the B3LYP/6-311++G** level, we find the gauche conformer is slightly more stable, with the energy difference between two conformers determined to be only 65 cm(-1). In our photoelectron spectra, the vertical ionization potential (IP) for the cis conformer of propanal was then determined to be 9.999 (+/-0.003) eV, while that of the gauche conformer of propanal was estimated to be 9.944 eV. A long vibrational progression in the in-plane CCCO deformation vibrational mode, v, for the cis conformer is systematically observed in all photoelectron spectra in which this mode is excited, suggesting that the geometry of the ground ionic state is significantly different from that of the 3s Rydberg state, particularly along the v(15) coordinates.