Synthesis and photoluminescence properties of π-extended fluorene derivatives: the first example of a fluorescent solvatochromic nitro-group-containing dye with a high fluorescence quantum yield

Functional π-extended fluorene derivatives, 2,7-di(p-substituted-phenyl)fluorenes containing different functional groups such as hydrogen, trimethylsilyl (TMS), methoxycarbonyl, cyano, and nitro groups, were synthesized. Except for the nitro group, the resulting compounds exhibited extremely high fluorescence quantum yields (ΦF >0.85 in chloroform). The diphenylfluorene containing nitro groups have higher fluorescence quantum yield (ΦF = 0.31 in N,N’-dimethyl-formamide) than other nitro-group-containing fluorophores which were previously reported (ΦF <0.1). Furthermore, this compound exhibited large Stokes’ shift with green to orange emission and unique on–off behavior of the emission by solvents.