Fluorene Substitution

The series of Zn(II) complexes with 1-amidino-3-aryl-substituted-thioureas [121], acetamidomalondihydroxymate [122], benzilbisthiosemicarbazone [123], novel fluorene-substituted terpyridine [124], per-fluoroalkoxy-substituted phthalocyanine [125], and 3-carboxylacetonehydroxamic acid [126] were synthesized. The behavior of these complexes was investigated by spectroscopic and electrochemical methods. 

Omer KM, Ku S-Y, Wong K-T, Bard AJ (2009) Efficient and stable blue electrogenerated chemiluminescence of fluorene-substituted aromatic hydrocarbons. Angew Chem Int Ed 48(49) 9300-9303... 

Studies [41,47] have demonstrated that polyimides derived from ether-bridged aromatic diamines with -CF3 groups are soluble, high-temperature polymer materials with low moisture absorption, low dielectric constant, high optical transparency, and low birefringence. The effect of fluorene substitution on the dielectric constant of polyimides has been demonstrated for a broad spectrum of fluorene-containing diamine structures (Table 3.2). The... 

Fluorine substitution generally substantially reduced the dielectric constant in cases with symmetric substitution. It was estimated that around 50% of the observed decreasing trend in the dielectric constant versus the percentage of fluorene can be attributed to a reduction in absorbed moisture as the result of an increase in hydrophobicity. The remaining 50% can be apportioned, on average, between the increased free volume (approximately 25%) and reduced total polarizability (approximately 25%). Little effect of fluorene substitution on dynamic thermal or thermo-oxidative stability was observed for a series of fluorinated polyimides [48]. Low dielectric constant polyimides and low water absorption polyimides were reported by several researchers [49-51]. The correlation between a high free volume and dielectric constant in polyimides has been previously reported in the literature [52]. 

---