The lately postulated Å resolution induced by (non-)resonant chemical interaction as well as by charge-transfer phenomena in plasmon-enhanced spectroscopies, i.e. in tip-enhanced Raman spectroscopy, was evaluated by a full quantum chemical approach.

Experimental evidence suggests an extremely high, possibly even sub-molecular, spatial resolution of tipenhanced Raman spectroscopy (TERS). While the underlying mechanism is currently still under discussion, two main contributions are considered: The involved plasmonic particles are able to highly confine light to small spatial regions in the near-field, i.e. the electromagnetic effect, and the chemical effect due to altered molecular properties of the sample in close proximity to the plasmonic tip. Significant theoretical effort is put into the modelling of the electromagnetic contribution by various groups. In contrast, we previously introduced a computational protocol that allows for investigation of the local chemical effect -including nonresonant, resonant and charge transfer contributions -in a plasmonic hybrid system by mapping the sample molecule with a metallic tip model at the (time-dependent) density functional level of theory. In the present contribution, we evaluate the impact of static charges localized on the tip's frontmost atom, possibly induced by the tip geometry in the vicinity of the apex, on the TERS signal and the lateral resolution. To this aim, an immobilized molecule, i.e. tin(II) phthalocyanine (SnPc), is mapped by the plasmonic tip modeled by a single positively vs. negatively charged silver atom. The performed quantum chemical simulations reveal a pronounced enhancement of the Raman intensity under non-resonant and resonant conditions with respect to the uncharged reference system, while the contribution of charge transfer phenomena as well as of locally excited states of SnPc is highly dependent on the tip's charge.

The ring‐opening polymerization (ROP) of lactones is mainly catalyzed by tin(II) octanoate Sn(Oct)2, due to its efficiency and easy handling despite the toxic issues of tin. Herein, two novel dinuclear bis(β‐diketiminate) complexes with flexible alkylene bridging groups (1,2‐ethylene and 1,3‐propylene) and biocompatible zinc centers are introduced. The complexes are obtained by deprotonation of the protio‐ligands with Zn(HMDS)2 and fully characterized. Afterwards the complexes are studied regarding their catalytic activity towards the ROP of caprolactones. Briefly, ε‐caprolactone (CL), ε‐phenyl‐ε‐caprolactone (phCL) and ε‐methyl‐ε‐caprolactone (meCL) with and without benzyl alcohol (BnOH) as initiator in toluene are homopolymerized and compared to the known dinuclear 1,4‐phenylene bridged bis(β‐diketiminate) zinc catalyst and the mononuclear counterpart. Thereby, the catalysts are classified upon their efficiency by in situ IR measurements, selectivity, and polymerization control by size exclusion chromatography (SEC) of samples, which are terminated at 60% conversion. The novel zinc catalysts prevent Sn(Oct)2 typical molar mass broadening, show slower reaction rates than 1,4‐phenylene bridged bis(β‐diketiminate) and improve control compared to the mononuclear relative. However, a drastic loss of polymerization control resulting in high molar masses and polydispersities occurrs in the absence of BnOH. Furthermore, these complexes allow the ROP of phCL but are inactive for meCL.