Femtosecond Hot-Exciton Emission in a Ladder-Type pi-Conjugated Rigid-Polymer Nanowire

A hot-exciton is usually the initial elementary excitation product of the solid phase, particularly in low dimensional photonic materials, which is a bottle-neck to all subsequent processes. Measurement of hot-exciton emission (HExEm) is a great challenge due to fast EK relaxation and thus very weak transient emission. Here we report the first unambiguous observation of femtosecond HExEm from thin films of a model quasi-one-dimensional {\pi}-conjugated organic rigid-rod quantum nanowire, MeLPPP (methyl-substituted ladder-type poly(para-phenylenes), by using femtosecond time-resolved fluorescence spectroscopy. The results show the clear HExEm from the cooling hot-excitons has a lifetime of ~500 to ~800 fs, and concomitant very weak density-dependent singlet-singlet annihilation (SSA) due to this ultrashort dwelling time.