Utilizing Selective Chlorination to Synthesize New Triangulenium Dyes.

Functionalization of new sites on the triangulenium structure has been achieved by early-stage chlorination with N-chlorosuccinimide (NCS), giving rise to two new triangulenium dyes (1 and 3). By introducing the chlorine functionalities in the acridinium precursor, positions complementary to those previously obtained by electrophilic aromatic substitution on the final dyes are accessed. The chlorination is selective, giving only one regioisomer for both mono- and dichlorination products. For the monochlorinated acridinium compound, a highly selective ring-closing reaction was discovered, generating a single regioisomer of the cationic [4]helicene product. Further investigations into the mechanism of the [4]helicene formation lead to the first isolation of the previously proposed intermediate of the two-step SNAr reaction, key to all aza-bridged triangulenium and helicenium systems. Late-stage functionalization of DAOTA+ with NCS gave rise to a different dichlorinated compound (2). The fully ring closed chlorinated triangulenium dyes 1, 2, and 3 show a redshift in absorption and emission, while maintaining relatively high fluorescence quantum yields of 36%, 26%, and 41% and long fluorescence lifetimes of 15, 12.5, and 16 ns, respectively. Cyclic voltammetry shows that chlorination of the triangulenium dyes significantly lowers reduction potentials and thus allows for efficient tuning of redox and photoredox properties.

Crystal structure and optical properties of a two-sited EuIII compound: an EuIII ion coordinated by two [EuIII(DOTA)]- complexes (DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate).

The structure and solid-state luminescence properties of an EuIII compound with two different lanthanide sites, [Eu(µ-O)5(OH)(H2O)2][Eu(DOTA)(H2O)]2 (DOTA is 1,4,7,10-tetrazacyclododecane-1,4,7,10-tetraacetate, C16H24N4O8), were determined. The compound crystallizes in a laminar structure in the triclinic space group P-1, where the two sites are a free europium(III) ion and an [Eu(DOTA)(H2O)]- complex. The crystal structure was determined using complex data treatment due to nonmerohedral twinning. Experimental data sets were recorded with large redundancy and separated according to scattering domains in order to obtain a reliable structure. In the first site, the [Eu(DOTA)(H2O)]- complex was found to adopt a capped twisted square-antiprismatic (cTSAP) conformation, where a capping water molecule increased the coordination number of the europium(III) site to nine (CN = 9). In the second site, the europium(III) ion was found to be coordinated by two water molecules, one hydroxide group and five oxide groups from neighbouring [Eu(DOTA)(H2O)]- complexes. The coordination geometry of this site was found to be a compressed square antiprism (SAP) and the coordination number of the europium(III) ion was found to be eight (CN = 8). A large increase in the rate constant of luminescence was observed for EuIII in [Eu(DOTA)(H2O)]- in solid-state luminescence spectroscopy measurements compared to in solution, which led to investigations of single crystals in deuterated media to exclude additional effects of quenching. We conclude that the most probable cause of the decrease in the observed luminescence lifetimes is the high asymmetry of the coordination environment of [Eu(DOTA)(D2O)]- in the [Eu(µ-O)5(OD)(D2O)2][Eu(DOTA)(D2O)]2 crystals.