Raman antenna effect from exciton–phonon coupling in organic semiconducting nanobelts

Abstract

The highly anisotropic interactions in organic semiconductors together with the soft character of organic materials lead to strong coupling between nuclear vibrations and exciton dynamics, which potentially results in anomalous electrical, optical and optoelectrical properties. Here, we report on the Raman antenna effect from organic semiconducting nanobelts 6,13-dichloropentacene (DCP), resulting from the coupling of molecular excitons and intramolecular phonons. The highly ordered crystalline structure in DCP nanobelts enables the precise polarization-resolved spectroscopic measurement. The angle-dependent Raman spectroscopy under resonant excitation shows that all Raman modes from the skeletal vibrations of DCP molecule act like a nearly perfect dipole antenna I ∝ cos(θ - 90), with almost zero (maximum) Raman scattering parallel (perpendicular) to the nanobelt's long-axis. The Raman antenna effect in DCP nanobelt is originated from the coupling between molecular skeletal vibrations and intramolecular exciton and the confinement of intermolecular excitons. It dramatically enhances the Raman polarization ratio (ρ = I/I > 25) and amplifies the anisotropy of the angle-dependent Raman scattering (κ = I/I > 12) of DCP nanobelts. These findings have crucial implications for fundamental understanding on the exciton-phonon coupling and its effects on the optical properties of organic semiconductors.

Exciton-Phonon Interaction and Relaxation Times from First Principles

“…Excitons pose new challenges to this framework, since one can no longer study independently the scattering of electrons or holes with phonons when the two carriers are bound together. Rather, the challenge is to address exciton-phonon (ex-ph) interactions, which govern exciton dynamics over a wide temperature range, regulating photoluminescence linewidths, exciton diffusion and ultrafast dynamics [32][33][34][35][36][37][38][39][40][41][42]. Several analytical or semiempirical models have been proposed for ex-ph interactions [43][44][45][46][47][48][49][50]; recent work has put forward a many-body approach but did not present numerical results [51].…”

Heterojunctions Derived by Integrating Arylene-Ethynylene Nanobelts and N-Doped Graphene for Molecular Sensing

“…9 For instance, the nanobelt structure of 6,13-dichloropentacene were successfully fabricated through molecular arrangement of the strong face-to-face interaction between the adjacent planar cores. 16 Oriented crystalline microribbons of 9anthracenecarboxylic acid were self-assembled through a solvent-evaporation method, and the microribbons were found to twist reversibly under uniform illumination conditions. 17 A photoactive anthracene derivative, dimethyl-2(3-(anthracen-9-yl)allylidene) malonate, was reported to be able to self-organize into single-crystal curling nanowires in a solvent-evaporation method.…”

“…The bottom-up approach can be an ideal alternative to arrangement of a large number of complex, small material units at low cost and in a less time-consuming way . For instance, the nanobelt structure of 6,13-dichloropentacene were successfully fabricated through molecular arrangement of the strong face-to-face interaction between the adjacent planar cores . Oriented crystalline microribbons of 9-anthracenecarboxylic acid were self-assembled through a solvent-evaporation method, and the microribbons were found to twist reversibly under uniform illumination conditions .…”

Dissipation dynamics of intrachain exciton coupled with phonons in MEH‐PPV: Time‐resolved multiplex coherent anti‐Stokes Raman scattering

“…Interest in optoelectronic semiconductor materials has increased rapidly in the last three decades. The exciton energy dissipation mechanism of the optoelectronic materials involving semiconductor quantum dots or organic materials has been the subject of intensive theoretical and experimental studies because it plays a distinctive role in the performance of optoelectronic devices. In these types of optoelectronic organic materials, the coupling between Frenkel exciton and phonon in the conjugated polymer would influence the photo‐physical and photo‐chemical processes involving the heat transport at molecular junction, the formation and transport of carriers in organic semiconductors, and the selectivity in single‐molecular chemistry .…”