Detection of Cu(ii) and NO by ‘on–off’ aggregation in poly(aryl ether) dendron derivatives

Abstract

We report the detection of Cu(II) and NO at micro and nano-molar concentrations, respectively, by poly(aryl ether) dendron derivatives containing anthracene moiety attached through an acylhydrazone ‘molecular loop’. In the absence of Cu(II), the acylhydrazone moiety undergoes cis–trans photo-isomerization, resulting in negligible emission from anthracene. Conversely, specific binding of Cu(II) by the acylhydrazone unit arrests the isomerization process and triggers aggregation of the molecules through hydrogen bonding and π–π interactions. The metal ion driven self-assembly leads to significant enhancement of the emission intensity from the anthracene excimer with a dendritic effect on the emission quantum yield (maximum Φ_{excimer emis.} ∼0.11 ± 0.01). The binding constants (log K) for the 1 : 1 complexes between the dendron derivatives and Cu(II) were determined using a fluorescence titration method and the values fall between 9.13 and 10.16. The Cu(II)–dendron systems were then exposed to nitric oxide (NO) along with other gases and the systems exhibit specific fluorescent ‘off’ signal towards NO at nano-molar concentrations. The mechanism of quenching was analyzed and the results suggest that the presence of NO leads to de-aggregation in the system.