Polyterthiophenes Cross‐Linked with Terpyridyl Metal Complexes for Molecular Architecture of Optically and Electrochemically Tunable Materials

Resonance Raman Excitation Profiles of Fe(II)-Terpyridine Complexes: Electronic Effects of Ligand Modifications

Metal 2,2':6',2″-terpyridine (tpy) complexes are readily used as building blocks in metallo-supramolecular polymers that stand out for their photophysical properties in solar energy assemblies. Furthermore, Resonance Raman (RR) excitation profiles are sensitive indicators of the electronic properties of chromophores. Previously, using RR spectroscopy, we studied the [Fe(tpy)₂]²⁺ complex and metallo-supramolecular polymers formed by tpy derivatives and Fe(II) ions. Here, we compare RR spectra of iron (Fe(II)) complexes with 4'-substituted tpy ligands─[Fe(4'-R-tpy)₂]²⁺, with R = H (1a), Cl (2a), 4-chlorophenyl (3a), and 2-thienyl (4a) to describe changes in their electronic structure after functionalization. By combining theoretical calculations, RR, and UV/vis spectra, we elucidated differences in the RR excitation profiles of 1a, 2a, and 4a complexes. In all Raman modes, complexes 1a and 2a showed maximal enhancement only at 532 nm excitation, whereas complex 4a exhibited maximal enhancement selectively at either 532 or 633 nm excitations. Based on our calculations, the mixed metal/ligand character of the highest occupied molecular orbital (HOMO) of 4a complex manifests itself through selective enhancement of vibration modes, mainly localized on the 2-thienyl unit at 633 nm excitation, which may explain the unique behavior of this complex. Therefore, complex 4a is a prospective candidate for further detailed photophysical explorations toward developing sensitizers for solar cells.

Reliable environmental trace heavy metal analysis with potentiometric ion sensors - reality or a distant dream

Over two decades have passed since polymeric membrane ion-selective electrodes were found to exhibit sufficiently lower detection limits. This in turn brought a great promise to measure trace level concentrations of heavy metals using potentiometric ion sensors at environmental conditions. Despite great efforts, trace analysis of heavy metals using ion-selective electrodes at environmental conditions is still not commercially available. This work will predominantly concentrate on summarizing and evaluating prospects of using potentiometric ion sensors in view of environmental determination of heavy metals in on-site and on-line analysis modes. Challenges associated with development of reliable potentiometric sensors to be operational in environmental conditions will be discussed and reasoning behind unsuccessful efforts to develop potentiometric on-site and on-line environmental ion sensors will be explored. In short, it is now clear that solely lowering the detection limit of the ion-selective electrodes does not guarantee development of successful sensors that would meet the requirement of environmental matrices over long term usage. More pressing challenges of the properties and the performance of the potentiometric sensors must be addressed first before considering extending their sensitivity to low analyte concentrations. These are, in order of importance, selectivity of the ion-selective membrane to main ion followed by the membrane resistance to parallel processes, such as water ingress to the ISM, light sensitivity, change in temperature, presence of gasses in solution and pH and finally resistance of the ion-selective membrane to fouling. In the future, targeted on-site and on-line environmental sensors should be developed, addressing specific environmental conditions. Thus, ion-selective electrodes should be developed with the intention to be suitable to the operational environmental conditions, rather than looking at universal sensor design validated in the idealized and simple sample matrices.