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

TL;DR

This paper reports the first direct observation of femtosecond hot-exciton emission in a ladder-type pi-conjugated nanowire, revealing ultrafast exciton cooling and weak singlet-singlet annihilation effects.

Contribution

It provides the first unambiguous measurement of femtosecond hot-exciton emission in a quasi-one-dimensional organic nanowire using femtosecond time-resolved fluorescence spectroscopy.

Findings

Hot-exciton emission lifetime of 500-800 fs

Ultrashort hot-exciton dwelling time reduces singlet-singlet annihilation

First direct observation of femtosecond hot-exciton emission in this material

Abstract

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.