Primary Photoprocesses in Thionine in Supramolecular Complexes with Cucurbit[7,8]urils in Water

Thionine (ThH⁺) molecules form monomeric ThH⁺@CB7 (1: 1) and dimeric 2ThH⁺@CB8 (2: 1) complexes with cucurbit7,8]urils (CB7) and (CB8) in water. Unlike the case free ThH⁺ molecules, the absorption spectrum of the complexes is characterized by a hypsochromic shift of the maximum by 6 and 41 nm for ThH⁺@CB7 and 2ThH⁺@CB8, respectively. The ThH⁺@CB7 complexes exhibit fluorescence, unlike the nonfluorescing 2ThH⁺@CB8 complexes. The monomeric complexes undergo intersystem crossing to the triplet state with a lifetime of 14 μs. The dimeric complexes have a very low quantum yield of the triplet state. The triplet state of the dimeric complexes was populated by photosensitized excitation by triplet–triplet energy transfer. The lifetime of the triplet state is ≈50 μs.