Johan Hjelm

Two-photon excitation and time-resolved fluorescence: I. The proper response function for analysing single-photon counting experiments

An accurate instrumental response function is needed to deconvolute fluorescence data obtained by time-correlated single-photon counting (TCSPC) upon multi-photon excitation. Hitherto the response function was obtained by measuring Rayleigh scattering (RS) from colloidal solutions, as is also used in one-photon excited fluorescence. We show that hyper Rayleigh scattering (HRS) provides a better choice for deconvolution of fluorescence decays, as obtained by TCSPC and two-photon excitation (TPE). The one- and two-photon response functions were monitored as RS and HRS from colloidal gold particles at 800 and 400 nm, respectively.

A rod-like polymer containing {Ru(terpy)2} units prepared by electrochemical coupling of pendant thienyl moieties

A new rod-like coordination polymer consisting of (Ru-(terpy)2) motifs bridged by bithiophene units has been prepared by electrochemical polymerisation in acidic organic medium.

Solvent effects on charge transport through solid deposits of [Os(4,4′-diphenyl-2,2′-dipyridyl)2Cl2]

Mechanically attached, solid-state films of [Os(4,4-diphenyl-2,2-dipyridyl)2Cl2] have been formed on gold macro- and microelectrodes and their voltammetric properties investigated. The voltammetric response of these films associated with the Os(2+/3+) redox reaction is reminiscent of that observed for an ideal reversible, solution phase redox couple only when the contacting electrolyte contains of the order of 40% v/v of acetonitrile (ACN). The origin of this effect appears to involve preferential solvation of the redox centres by acetonitrile which facilitates the incorporation of charge compensating counterions. Scanning electron microscopy reveals that voltammetric cycling in 40:60 ACN-H2O containing 1.0 M LiClO4 as the electrolyte induces the formation of microcrystals. Voltammetry conducted under semi-infinite linear diffusion conditions has been used to determine the apparent diffusion coefficient, Dapp, for homogeneous charge transport through the deposit. The dynamics of charge transport decrease with increasing film thickness but appear to increase with increasing electrolyte concentration. These observations suggest that ion transport rather than the rate of electron self-exchange limit the overall rate of charge transport through these solids. When in contact with 40:60 ACN-H2O containing 1.0 M LiClO4 as electrolyte, Dapp values for oxidation and reduction are identical at 1.7 +/- 0.4 x 10(-12) cm2 s(-1). In the same electrolyte, the standard heterogeneous electron transfer rate constant, k(o), determined by fitting the full voltammogram using the Butler-Volmer formalism, is 8.3 +/- 0.5 x 10(-7) cm s(-1). The importance of these results for the rational design of solid state redox active materials for battery, display and sensor applications is considered.

Electropolymerisable bipyridine ruthenium(II) complexes. Synthesis and electrochemical characterisation of 4-(3-methoxystyryl)- and 4,4'-di(3-methoxystyryl)-2,2'-bipyridine ruthenium complexes

A number of new ruthenium polypyridyl complexes with mono- or di-(3-methoxystyryl) substituted bipyridines have been synthesized. The complexes were characterised by NMR, elemental analysis, UV-vis absorption and emission spectroscopy, and cyclic voltammetry. Electroactive polymer films of these complexes have been prepared both by oxidative and reductive electropolymerisation. The polymers have been characterised by UV-vis absorption spectroscopy and cyclic voltammetry. Possible processes involved in the polymerisation and the structure of the film are discussed.

Tuning the properties of ruthenium bipyridine dyes for solar cells by substitution on the ligands—characterisation of bis[4,4′-di(2-(3-methoxyphenyl)ethenyl)-2,2′-bipyridine][4,4′-dicarboxy-2,2′-bipyridine]ruthenium(II) dihexafluorophosphate

The new dye complex bis[4,4′-di(2-(3-methoxyphenyl)ethenyl)-2,2′-bipyridine][4,4′-dicarboxy-2,2′-bipyridine]ruthenium(II) dihexafluorophosphate (1) has been prepared, characterised by absorption spectroscopy and adsorbed onto nanocrystalline TiO2 electrodes. The resulting system was studied by absorption spectroscopy, electrochemistry and photoelectrochemistry and the results were compared to those for a reference system with bis[2,2′-bipyridine][4,4′-dicarboxy-2,2′-bipyridine]ruthenium(II) n(2). The system with 1 displays a broader and red-shifted UV-vis absorption compared to that with 2. Moreover, the system with 1 is less sensitive towards the water content in the electrolyte, and an adsorbed monolayer of 1 remains on the electrode surface after days even in aqueous NaOH (0.1 M), while 2 desorbs immediately.