Regio- and stereospecific [2+2] photocyclodimerization of a crown-containing butadienyl dye via cation-induced self-assembly in solution / E.N. Ushakov, A.I. Vedernikov, M.V. Alfimov, S.P. Gromov // Photochemical & Photobiological Sciences. – 2011. – Т. 10. – № 1. – P. 15-18