Supramolecular control of phthalocyanine dye aggregation

A phthalocyaninato zinc(II) dye with four peripheral N-methylpyridinium anchor groups and its higher-order complex with cucurbit[7] uril were photophysically characterised. The supramolecular host-guest interaction with the anchor yielded a deaggregation of the dye in neutral water solutions. This was signalised by the formation of a sharp UV-vis absorption band at ca. 690 nm and a dramatic increase in the fluorescence. While the aggregated dye is essentially non-fluorescent (Phi(f)< 2 x10(-3)), the supramolecular complex with cucurbit[7] uril shows an emission quantum yield of Phi(f) = 2.7 x 10(-2). The apparent 1: 1 binding constant of each pyridinium anchor unit was determined as K=7.4x10(4) M-1. Competitors such as polyamines (e. g. spermine), and also metal cations, reverse the complexation. This can be followed by the decrease in the fluorescence signal and the disappearance of the characteristic UV-vis absorption signature of the deaggregated dye. The effect was used to investigate the binding of 11 metal cations (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Zn2+, Eu3+, Gd3+). Cations with multiple charges and a large ionic radius are found to form the strongest complexes with cucurbit[7]uril (K>1x10(3) M-1 for Ca2+, Sr2+, Eu3+).