Alignment enhancement of molecules embedded in helium nanodroplets by multiple laser pulses

We show experimentally that field-free one-dimensional (1D) alignment of 1,4-diiodobenzene molecules embedded in helium nanodroplets, induced by a single, linearly polarized 200-fs laser pulse, can be significantly enhanced by using two or four optimally synchronized laser pulses. The strongest degree of 1D alignment is obtained with four pulses and gives ⟨cos2θ⟩>0.60. Besides the immediate implications for molecular frame studies, our results pave the way for more general manipulation of rotational motion of molecules in He droplets

Microsolvation in superfluid helium droplets studied by the electronic spectra of six porphyrin derivatives and one chlorine compound

After almost two decades of high resolution molecular spectroscopy in superfluid helium droplets, the understanding of microsolvation is still the subject of intense experimental and theoretical research. According to the published spectroscopic work including microwave, infrared, and electronic spectroscopy, the latter appears to be particularly promising to study microsolvation because of the appearance of pure molecular transitions and spectrally separated phonon wings. Instead of studying the very details of the influence of the helium environment for one particular dopant molecule as previously done for phthalocyanine, the present study compares electronic spectra of a series of non-polar porphyrin derivatives when doped into helium droplets consisting of 104–105 helium atoms. Thereby, we focus on the helium-induced fine structure, as revealed most clearly at the corresponding electronic origin. The interpretation and the assignment of particular features obtained in the fluorescence excitation spectra are based on additional investigations of dispersed emission spectra and of the saturation behavior. Besides many dopant-specific results, the experimental study provides strong evidence for a particular triple peak feature representing the characteristic signature of helium solvation for all seven related dopant species

Electronic spectroscopy of 9,10-dichloroanthracene inside helium droplets

The spectroscopy of molecules doped into superfluid helium droplets provides information on both, the dopant molecule and the helium environment. Electronic spectra of 9,10-dichloroanthracene in helium droplets are presented and compared with corresponding gas phase spectra to unravel the influence of the helium environment. The combined investigation of fluorescence excitation and dispersed emission provides information on dynamic processes in addition to energetic conditions. For vibronic states, the helium induced decay channels dominate over all intramolecular channels that contribute to the gas phase behavior. In addition to the triplet splitting caused by the Cl isotopes, a fine structure resolved for all transitions in the fluorescence excitation spectrum was found, which is the signature of microsolvation of this compound in helium droplets. This fine structure is identified as a single pure molecular transition accompanied by a sharply structured phonon wing. The corresponding fine structure measured for bare anthracene shows remarkable differences

Triplet state properties of [Os(phen)₂(dppene)]²⁺ in different host materials and host to guest energy transfer in PVK

Emission properties of [Os(phen)₂(dppene)]²⁺ were investigated from 1.4 to 300 K in ethanol, PMMA, and PVK, a matrix which is frequently applied in OLEDs. These data provide the zero-field splitting values of the emitting T₁ state and the individual decay times of its substates. The T₁ state is assigned to be largely of MLCT character. The splittings change only moderately due to variation of the matrix, whereas the individual decay times are substantially affected. Further, energy transfer from the triplet state of PVK to [Os(phen)₂(dppene)]²⁺ was studied by applying time-resolved emission spectroscopy and is assigned to be dominantly of Dexter type

Understanding the quantum nature of low-energy C(3Pj) + He inelastic collisions

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Exceptional oxygen sensing capabilities and triplet state properties of Ir(ppy-NPh₂)₃

Cyclometalated Ir(III) complexes are excellent triplet emitters used in efficient OLEDs and sensing devices. These materials are also the subject of several spectroscopic and theoretical investigations. The potential for applications of Ir(III) complexes in optical devices is determined by their electronic structures. The unique excited-state properties of Ir(III) complexes make these compounds particularly suitable for applications in oxygen sensing, e.g., for aerodynamic measurements and biomedical imaging. Therefore, it is important to study the electronic properties of these complexes in detail and to investigate the possibilities of tuning and optimizing the emission behavior, for example, by substitution of known compounds. In particular, the substitution of ppy ligands of Ir(ppy)₃ by ppy-NPh₂ has distinct effects on the photoluminescence behavior, such as energy shifts, changes in the emission decay time, and quantum yields. Moreover, the substitution leads to an effective shielding of the emitting core and - what is very important - makes the compound soluble in organic solvents. Synthesis and electroluminescence properties of Ir(ppy-NPh₂)₃ and related compounds have already been reported