Structures and IR/UV spectra of neutral and ionic phenol-Ar-n cluster isomers (n <= 4): competition between hydrogen bonding and stacking

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The structures, binding energies, and vibrational and electronic spectra of various isomers of neutral and ionic phenol–Arnclusters with n ≤ 4, PhOH(+)–Arn, are characterized by quantum chemical calculations. The properties in the neutral and ionic ground electronic states (S0, D0) are determined at the M06-2X/aug-cc-pVTZ level, whereas the S1 excited state of the neutral species is investigated at the CC2/aug-cc-pVDZ level. The Ar complexation shifts calculated for the S1 origin and the adiabatic ionisation potential, ΔS1 and ΔIP, sensitively depend on the Ar positions and thus the sequence of filling the first Ar solvation shell. The calculated shifts confirm empirical additivity rules for ΔS1 established recently from experimental spectra and enable thus a firm assignment of various S1 origins to their respective isomers. A similar additivity model is newly developed for ΔIP using the M06-2X data. The isomer assignment is further confirmed by Franck–Condon simulations of the intermolecular vibrational structure of the S1 ← S0 transitions. In neutral PhOH–Arn, dispersion dominates the attraction and π-bonding is more stable than H-bonding. The solvation sequence of the most stable isomers is derived as (10), (11), (30), and (31) for n ≤ 4, where (km) denotes isomers with k and m Ar ligands binding above and below the aromatic plane, respectively. The π interaction is somewhat stronger in the S1 state due to enhanced dispersion forces. Similarly, the H-bond strength increases in S1 due to the enhanced acidity of the OH proton. In the PhOH+–Arn cations, H-bonds are significantly stronger than π-bonds due to additional induction forces. Consequently, one favourable solvation sequence is derived as (H00), (H10), (H20), and (H30) for n ≤ 4, where (Hkm) denotes isomers with one H-bound ligand and k and m π-bonded Ar ligands above and below the aromatic plane, respectively. Another low-energy solvation motif for n = 2 is denoted (11)H and involves nonlinear bifurcated H-bonding to both equivalent Ar atoms in a C2v structure in which the OH group points toward the midpoint of an Ar2 dimer in a T-shaped fashion. This dimer core can also be further solvated by π-bonded ligands leading to the solvation sequence (H00), (11)H, (21)H, and (22) for n ≤ 4. The implications of the ionisation-induced π → H switch in the preferred interaction motif on the isomerisation and fragmentation processes of PhOH(+)–Arn are discussed in the light of the new structural and energetic cluster parameters

Microsolvation of the acetanilide cation (AA(+)) in a nonpolar solvent: IR spectra of AA(+)-L-n clusters (L = He, Ar, N-2; n <= 10)

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Infrared photodissociation (IRPD) spectra of mass-selected cluster ions of acetanilide (N-phenylacetamide), AA+–Ln, with the ligands L = He (n = 1–2), Ar (n = 1–7), and N2 (n = 1–10) are recorded in the hydride stretch (amide A, νNH, νCH) and fingerprint (amide I–III) ranges of AA+ in its 2A′′ ground electronic state. Cold AA+–Ln clusters are generated in an electron impact ion source, which predominantly produces the most stable isomer of a given cluster ion. Systematic vibrational frequency shifts of the N–H stretch fundamentals (νNH) provide detailed information about the sequential microsolvation process of AA+ in a nonpolar (L = He and Ar) and quadrupolar (L = N2) solvent. In the most stable AA+–Ln clusters, the first ligand forms a hydrogen bond (H-bond) with the N–H proton of trans-AA+ (t-AA+), whereas further ligands bind weakly to the aromatic ring (π-stacking). There is no experimental evidence for complexes with the less stable cis-AA+ isomer. Quantum chemical calculations at the M06-2X/aug-cc-pVTZ level confirm the cluster growth sequence derived from the IR spectra. The calculated binding energies of De(H) = 720 and 1227 cm−1 for H-bonded and De(π) = 585 and 715 cm−1 for π-bonded Ar and N2 ligands in t-AA+–L are consistent with the observed photofragmentation branching ratios of AA+–Ln. Comparison between charged and neutral AA(+)–L dimers indicates that ionization switches the preferred ion–ligand binding motif from π-stacking to H-bonding. Electron removal from the HOMO of AA+ delocalized over both the aromatic ring and the amide group significantly strengthens the C[double bond, length as m-dash]O bond and weakens the N–H bond of the amide group

Ionization-induced pi -> H site switching dynamics in phenol-Ar-3

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Electronic excitation spectra of the S1 ← S0 transition obtained by resonance-enhanced two-photon ionization (REMPI) are analysed for phenol–Arn (PhOH–Arn) clusters with n ≤ 4. An additivity rule has been established for the S1 origin shifts upon sequential complexation at various π binding sites, which has allowed for the identification of two less stable isomers not recognized previously, namely the (2/0) isomer for n = 2 and the (2/1) isomer for n = 3. Infrared (IR) spectra of neutral PhOH–Arn and cationic PhOH+–Arnclusters are recorded in the vicinity of the OH and CH stretch fundamentals (νOH, νCH) in their S0 and D0 ground electronic states using IR ion dip spectroscopy. The small monotonic spectral redshifts ΔνOH of about −1 cm−1 per Ar atom observed for neutral PhOH–Arn are consistent with π-bonded ligands. In contrast, the IR spectra of the PhOH+–Arn cations generated by resonant photoionization of the neutral precursor display the signature of H-bonded isomers, suggesting that ionization triggers an isomerization reaction, in which one of the π-bonded Ar ligands moves to the more attractive OH site. The dynamics of this isomerization reaction is probed for PhOH+–Ar3 by picosecond time-resolved IR spectroscopy. Ionization of the (3/0) isomer of PhOH+–Ar3(3π) with three π-bonded Ar ligands on the same side of the aromatic ring induces a π → H switching reaction toward the PhOH+–Ar3(H/2π) isomer with a time constant faster than 3 ps. Fast intracluster vibrational energy redistribution prevents any H → π back reaction

Weak hydrogen bonding motifs of ethylamino neurotransmitter radical cations in a hydrophobic environment: infrared spectra of tryptamine(+)-(N-2)(n) clusters (n <= 6)

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Size-selected clusters of the tryptamine cation with N2 ligands, TRA+–(N2)n with n = 1–6, are investigated by infrared photodissociation (IRPD) spectroscopy in the hydride stretch range and quantum chemical calculations at the ωB97X-D/cc-pVTZ level to characterize the microsolvation of this prototypical aromatic ethylamino neurotransmitter radical cation in a nonpolar solvent. Two types of structural isomers exhibiting different interaction motifs are identified for the TRA+–N2 dimer, namely the TRA+–N2(H) global minimum, in which N2 forms a linear hydrogen bond (H-bond) to the indolic NH group, and the less stable TRA+–N2(π) local minima, in which N2 binds to the aromatic π electron system of the indolic pyrrole ring. The IRPD spectrum of TRA+–(N2)2 is consistent with contributions from two structural H-bound isomers with similar calculated stabilization energies. The first isomer, denoted as TRA+–(N2)2(2H), exhibits an asymmetric bifurcated planar H-bonding motif, in which both N2 ligands are attached to the indolic NH group in the aromatic plane via H-bonding and charge–quadrupole interactions. The second isomer, denoted as TRA+–(N2)2(H/π), has a single and nearly linear H-bond of the first N2 ligand to the indolic NH group, whereas the second ligand is π-bonded to the pyrrole ring. The natural bond orbital analysis of TRA+–(N2)2 reveals that the total stability of these types of clusters is not only controlled by the local H-bond strengths between the indolic NH group and the N2 ligands but also by a subtle balance between various contributing intermolecular interactions, including local H-bonds, charge–quadrupole and induction interactions, dispersion, and exchange repulsion. The systematic spectral shifts as a function of cluster size suggest that the larger TRA+–(N2)n clusters with n = 3–6 are composed of the strongly bound TRA+–(N2)2(2H) core ion to which further N2 ligands are weakly attached to either the π electron system or the indolic NH proton by stacking and charge–quadrupole forces

Ionization-induced pi -> H site-switching in phenol-CH4 complexes studied using IR dip spectroscopy

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.IR spectra of phenol–CH4 complexes generated in a supersonic expansion were measured before and after photoionization. The IR spectrum before ionization shows the free OH stretching vibration (νOH) and the structure of neutral phenol–CH4 in the electronic ground state (S0) is assigned to a π-bound geometry, in which the CH4 ligand is located above the phenol ring. The IR spectrum after ionization to the cationic ground state (D0) exhibits a red shifted νOH band assigned to a hydrogen-bonded cationic structure, in which the CH4 ligand binds to the phenolic OH group. In contrast to phenol–Ar/Kr, the observed ionization-induced π → H migration has unity yield for CH4. This difference is attributed to intracluster vibrational energy redistribution processes

Neue Urbane Produktion : ein Wegweiser für das Bergische Städtedreieck

Regionale Produkte sind im Trend. Kreative Manufakturen, offene Werkstätten und moderne Fertigungsmethoden verhelfen dem Handwerk in der Stadt zu einer Renaissance. Was ist daran eigentlich das Neue? Und warum schlummert darin so ein großes Potenzial für einen nachhaltigen Wohlstand und für lebenswerte Quartiere? Knapp drei Jahre beforschte, förderte und vernetzte ein Projektteam aus Utopiastadt, dem Wuppertal Institut und dem transzent die Pioniere einer neuen Produktivität in der Region. Nun ist es an der Zeit, Bilanz zu ziehen - und nach vorne zu schauen, wo am Horizont die Visionen einer lebenswerten und produktiven Stadt von Morgen greifbar werden. Der vorliegende Wegweiser ist die Essenz aus drei Jahren Forschung, Praxis und Dialog. Er weist eine neue Richtung für die Region und ihre gestaltenden Akteure. Ob Wirtschaftsförderung, Stadtverwaltung, Zivilgesellschaft, Gründerszene, Unternehmen oder Wissenschaft: Wir laden dazu ein, den Weg gemeinsam zu beschreiten