Jl. Pozzo et al., SPIRO[2H]-1-BENZOPYRAN-2,9'-FLUORENES - HYPERCHROMIC AND BATHOCHROMICSHIFTS OF THE VISIBLE ABSORPTION OF CHROMENES, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 297, 1997, pp. 255-262
The synthesis of spiro[fluorene-naphthopyrans] and spiro[fluorene-fura
no[3,2-f]chromenes] allowed us to quantify the role of fluorene moiety
towards photochromic properties. Compared to corresponding diphenylch
romenes, the extended Pi system delocalization causes a bathochromic s
hift of the visible absorption of the colored merocyanines. Whatever t
he right hand side in the studied series, an hyperchromic effect is ob
served.