Observation of stimulated emission and ultrafast transient absorption dynamics from a novel alkyl-substituted PPV

Ultrafast transient absorption, stimulated emission (SE), and photoluminescence (PL) measurements were performed on solid films of the conducting polymer: poly[2-butyl-5-(2′-ethyl-hexyl)-1,4-phenylenevinylene](BuEH-PPV). The ground state absorption and luminescence of BuEH-PPV are similar to those of unsubstituted PPV, indicating that alkyl substitution does not significantly alter the electronic structure of the ground state. The PL lifetime and PL quantum yield of BuEH-PPV, however, are ≥ 900 ps and over 0.6, respectively. These numbers are nearly 3 times longer and higher than those for unsubstituted PPV. Moreover, BuEH-PPV exhibits a strong, relatively long-lived SE (≥ 60 ps). The SE decays more quickly than the PL due to an interfering photoinduced absorption which undergoes a dynamic blue-shift to mask the SE at later times. These observations taken together offer a prescription for controlling the excited state electronic structure of conjugated polymers, and open the possible production of optically or electrically pumped solid polymer lasers.