Design, Synthesis, Characteristics and Optical Properties of Two Pyridine/Fluorene Based Organic Ligands

Two pyridine/fluorene-based organic ligands 9-(2-chloropyridin-2-yl)-fluoren-9-ol (2-ClPyFOH) and 9-(6-bromopyridin-2-yl)-fluoren-9-ol (6-BrPyFOH) were synthesized successfully. The structures of the compounds were characterized detailedly by mass spectra and nuclear magnetic resonance. The most intense absorption peaks of 9-(pyridyl-2-yl)-fluoren-9-ol (PyFOH), 6-BrPyFOH, 2-ClPyFOH are 268/275/275, 275/275/275, 268/274/271, 268/274/271, and 268/275/271 nm in cyclohexane, dichloromethane, acetic ether, ethanol and acetonitrile, respectively, which shows the UV-vis of the compounds are red-shifted as the electron-withdrawing ability of halogenated pyridine segments in these solvents except acetic ether. The photoluminescence (PL) spectra peaks of the three compounds are 313/356/356, 327/358/365, 359/367/312, 316/316/401, and 386/377/438 nm in the five solvents, respectively. The PL spectra of PyFOH and 6-BrPyFOH are blue-shifted in ethanol solution compared to those in other lower polarity solvents, which is probably induced by their n-π^* electronic transition upon solvation derived from the pyridine segment. The PL spectra of 2-ClPyFOH is red-shifted in these solvents as the solvents polarity increasing except acetic ether. The bromine and chlorine at the 2-and 6-position of pyridine group would endow the ligands with different function units to provide various structures with especial characteristics.