The sensitivity of donor \u2013 acceptor charge transfer to molecular geometry in DAN \u2013 NDI based supramolecular flower-like self-assemblies

Mohammad Al Kobaisi,Sachin D Padghan,Sheshanath V Bhosale,Frank Antolasic,Shunichi Fukuzumi,Duong Duc La,Sidhanath V Bhosale,Lathe A Jones,Mohamed E El-Khouly,Rajesh S Bhosale

doi:10.1038/s41598-017-15599-9

Abstract

A charge-transfer (CT) complex self-assembled from an electron acceptor (NDI-EA: naphthalene diimide with appended diamine) and an electron donor (DAN: phosphonic acid-appended dialkoxynapthalene) in aqueous medium. The aromatic core of the NDI and the structure of DAN1 were designed to optimize the dispersive interactions (π-π and van der Waals interactions) in the DAN1–NDI-EA self-assembly, while the amino groups of NDI also interact with the phosphonic acid of DAN1 via electrostatic forces. This arrangement prevented crystallization and favored the directional growth of 3D flower nanostructures. This molecular geometry that is necessary for charge transfer to occur was further evidenced by using a mismatching DAN2 structure. The flower-shaped assembly was visualized by scanning electron and transmission electron microscopy. The formation of the CT complex was determined by UV-vis and cyclic voltammetry and the photoinduced electron transfer to produce the radical ion pair was examined by femtosecond laser transient absorption spectroscopic measurements.

Highlights

The field of organic optoelectronics has expanded dramatically in recent years, where systems including organic light-emitting devices (OLEDs) and organic photovoltaic (OPV) devices have shown great promise and rapid advances[1]
In the self-assemblies studied here, we show the hybridisation between the Molecular Orbital (MO) in the donor and acceptor molecules is ruled by the molecular geometry and orbital symmetry, which can result in an intricate overlap of charge densities of the two molecules in the complex to give a new set of frontier MOs and new optical and electronic features
The complex pattern in the Com[2] spectrum shows a low arrangement symmetry resulting from the twist in the π stacked alternating aromatic cores due to the hindrance applied by the strong electrostatic interaction of the periphery moieties, while the complementing geometry of the Com[1] resulted in much simpler spectrum[38]

Summary

Introduction

The field of organic optoelectronics has expanded dramatically in recent years, where systems including organic light-emitting devices (OLEDs) and organic photovoltaic (OPV) devices have shown great promise and rapid advances[1]. It is essential to understand the structure–properties relationships of these systems in order to design, optimize and control their photoelectronic functions. Such devices depend strongly on efficient charge separation in donor – acceptor systems. For example strong electron withdrawing moieties on the acceptor, such as fluorine, are combined with the substitution of strong electron donating moieties on the donor, such as thiophenes[24] This approach is used to design CT complexes with HOMO – LUMO gaps in the near infrared (NIR) and IR regions[25,26,27]. The simple NDI – DAN CT complexes studied here show HOMO – LUMO gaps just below 700 nm which can be further tuned to shift to lower energy

Methods

Results

Conclusion