Molecular Water Lilies: Orienting Single Molecules in a Polymer Film by Solvent Vapor Annealing

TL;DR

This paper introduces a macrocyclic fluorescent probe to measure molecular orientation and position in polymer films, demonstrating control via solvent vapor annealing, with implications for OLEDs and single-molecule spectroscopy.

Contribution

It presents a novel macrocyclic molecule as a probe for orientation and position measurement, and shows how solvent vapor annealing can control molecular placement in films.

Findings

Molecular orientation can be measured by photoluminescence modulation.

Molecular position is inferred from PL brightness analysis.

SVA causes molecules to accumulate at the polymer/air interface.

Abstract

The microscopic orientation and position of photoactive molecules is crucial to the operation of optoelectronic devices such as OLEDs and solar cells. Here, we introduce a shape-persistent macrocyclic molecule as an excellent fluorescent probe to simply measure (i) its orientation by rotating the excitation polarization and recording the strength of modulation in photoluminescence (PL), and (ii) its position in a film by analyzing the overall PL brightness at the molecular level. The unique shape, the absorption and the fluorescence properties of this probe yields information on molecular orientation and position. We control orientation and positioning of the probe in a polymer film by solvent vapor annealing (SVA). During the SVA process the molecules accumulate at the polymer/air interface, where they adopt a flat conformation, much like water lilies on the surface of a pond. The results are significant for OLED fabrication and single-molecule spectroscopy (SMS) in general.