LAUSR

Currently, molecular photonics of polymethine dyes (PDs) is the subject of many investigations. Usually, a low quantum yield of intersystem crossing [1–3] and the ability of dye molecules to form dimers as the simplest aggregates are the specific feature of PDs. Recently, we have found that the polymethine dyes 3,3'-diethylthiacarbocyanine and 3,3'-diethyl-5,5'dichloro-9-ethylthiacarbocyanine in water display delayed fluorescence in the presence of cucurbit[8]uril [4, 5]. The occurrence of delayed f luorescence indicates the formation of the triplet state, which is confirmed by measuring triplet–triplet absorption using laser kinetic spectroscopy. In the case of cucurbit[8]uril with a larger size of the cavitand cavity than cucurbit [7]uril, the formation of 2 : 1 and 2 : 2 host– guest complexes is possible as was shown for thiazole orange [6] and alkylsubstituted thiacarbocyanines [7]. It was found that 3,3'-dimethyland 3,3'-diethylthiacarbocyanines (MTCC and ETCC) in an aqueous solution in the presence of cucurbit[8]uril (CB8) form 2 : 2 dimeric complexes, which exhibit conventional (fast) f luorescence [7]. In this communication, we present the results of a study of delayed f luorescence of the 2MTCC@2CB8 and 2ETCC@2CB8 dimeric complexes. The spectra and decay kinetics of delayed fluorescence were measured on a Cary Eclipse Varian spectrofluorimeter at room temperature in air-saturated and oxygen-free solutions. Emission spectra were recorded in the phosphorescence detection mode. The delayed f luorescence and delayed-fluorescence excitation spectra for the 2MTCC@2CB8 complex in the oxygen-free aqueous solution are depicted in the figure 1. The delayed f luorescence spectrum coincides with the spectrum of fast f luorescence.