In connection with the synthetic studies of the cross-conjugated system 2, p-( diphenylhydroxymethyl) phenyltropolidene (13)* was prepared. On treatment with CF3COOH, 13 transformed to an aryltropylium ion (15) via an unstable blue colored compound. Based on NMR spectroscopy and some chemical properties the structure of the pigment is assumed to be diphenyl-p-tropylphenylmethyl cation (16) rather than the ...