Two-photon properties and excitation dynamics of poly(p-phenylenevinylene) derivatives carrying phenylanthracene and branched alkoxy pendents

This paper presents a study of excitation dynamics and two-photon properties in new branched poly(p-phenylenevinylene) structures which can be viewed as composed of interlinked structural units producing localized but interacting electronic excitations. Poly(p-phenylenevinylene) (PPV) derivatives, specifically poly[2-(9-phenylanthracen-10-yl)-1,4-phenylenevinylene] (P-1) and poly[2-(2-ethylhexyloxy)-5-(9-phenylanthracen-10-yl)-1,4-phenylenevinylene] (P-2), carrying 9-phenylanthracene pendent were prepared, and their one- and two-photon absorption and emission properties were studied in solution. P-1 and P-2 differ in structure by the presence of additional 2-ethylhexyloxy pendent groups in P-2. Both polymers were prepared by direct polymerization of the α,α'-dibromo-p-xylene monomers having the pendent group(s) in the present of excess potassium tert-butoxide. For the sake of comparison, 9,10-diphenylanthracene (DPA) and poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] [Meh-PPV (P-3)] were also included in our study. From nanosecond and femtosecond nonlinear transmission measurements, their effective two-photon cross sections (σ_TPA) at ∼ 800 nm were found to be 11.9 × 10^-20 for P-1, 66.6 × 10^-20 for P-2, and 44.0 × 10^-20 for P-3 in nanosecond pulses and 0.074 × 10^-20 for P-1, 0.196 × 10^-20 for P-2, and 0.168 × 10^-20 cm⁴/GW for P-3 in femtosecond pulses, respectively. Their two-photon excitation spectra were also studied. P-2 having both the phenylanthrace and alkoxy pendents exhibits the best performance as a two-photon absorber in both of nano- and femtosecond measurements at ∼800 nm. Furthermore, a complete energy transfer from the pendent phenylanthracene moiety to the PPV backbone is observed.