Poly (p-phenylene) with rationally designed urea groups was demonstrated to be a selective turn-on/off fluorescent anion sensor. Poly(p-phenylene) with [bis(trifluoromethyl)phenyl]urea pendants (poly-1  ) was prepared by Suzuki-Miyaura polycondensation reaction. In DMF poly-1  exhibited fluorescence quenching (turn-off) by the addition of F-. In contrast, by the addition of Cl-, poly-1  showed the fluorescence enhancement (turn-on). Time-dependent Density Functional calculations on model molecules of poly-1  imply that the energy levels of the first and the second excited singlet states locate near each other (ca. 1000 ~ 2000 cm-1), and these energy levels are forced to inverse by the coordination of F- to the urea group. Along with the energy-level inversion, the bis(trifluoromethyl)phenyl plane rotated by ca. 20 degree with respect to the urea-group plane. The breakdown of the local planar symmetry suggests that the presence of vibronic (pseudo Jahn-Teller) interaction between S1 and S2 along this rotational coordinate.

Vibronic switching of fluorescence output from urea-functionalized poly (p-phenylene) receptor by fluoride-anion recognition

245th National Meeting (2013)

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