Novel spiro-fluorenes from tandem radical addition for liquid crystalline monodisperse conjugated oligomers

3'-Nonafluorobutylmethyl-4'-methyl-spiro[cyclopentyl-9,1']fluorenes were successfully synthesized @@ivia@ tandem radical-addition reactions between 9,9-diallylfluorenes and perfluorobutyl iodide in the presence of a radical initiator followed by reduction under mild conditions. Single crystal analysis indicates that two substituents at 3,4-positions of cyclopentane are in a maleinoid form. Accordingly, four oligo(fluorene-@@ico@-bithiophene)s with the same molecular length of 610 run (7 fluorene units and 12 thiophene units) containing one to three novel spiro-fluorene units were synthesized. The introduction of the spiro-fluorene units results in noticeable enhancement of both glass transition temperature (@iT@dg) and clearing point temperature (@iT@dc) of the oligomers, but has little effect on their photophysical properties. Exchanging three 9,9-dioctylfluorene units with 3'-nonafluorobutylmethyl-4'-methyl-spiro[cyclopentyl-9,1'] fluorene units results in a 37'C enhancement of @iT@dg and a 61 'C enhancement of @iT@dc. All these results indicate that this new spiro-fluorene unit is an attractive building block for liquid crystalline conjugated polymers/oligomers with both high @iT@dg and @iT@dc.