Molecular motion of phosphazene-bound nonlinear optical chromophores

The behavior of nonlinear optical (NLO) groups linked to a polyphosphazene chain was studied by solid-state NMR spectroscopy. A series of poly(organophosphazenes) was prepared with the general structure [NP(RN(CH3)C6H4NO2)(x){O(CH2CH2O)(2)CH3}(2-x)](n), where x < 0.5 and the spacer group R = O(CH2)(2), O(CH2)(6), or OCH2(2-pyrrolidino), in addition to. the stilbene-containing polyphosphazene [NP{O(CH2)(2)N(CH3)C6H4CH=CHC6H4NO2}(0.4){O(CH2CH2O)(2)CH3}(1.6)](n). Structural characterization for the above polymers was achieved by P-31 NMR spectroscopy, differential scanning calorimetry, and elemental microanalysis. (Methoxyethoxy)ethoxy (MEE) cosubstituent poly(organophosphazenes) bearing O(CH2)(2)N(CH3)C6H4NO2 and O(CH2)(6)N(CH3)C6H4NO2 side groups were selected for study by room-temperature and variable-temperature solid-state P-31 and C-13 NMR-spectroscopy. The variable-temperature solid-state C-13 NMR spectra indicated that the use of a longer spacer group between the polymer backbone and the aromatic portion of the NLO side group lowers the temperature at which chromophore motion is quenched. This implied that the use of such structures may accelerate the randomization of NLO side group orientation at ambient temperatures following poling. This behavior was mirrored in the solid-state variable-temperature P-31 NMR spectra, which suggested that side chain and polymer backbone motion may be coupled.