Could you explain the significance of your article to the non-specialist?

Dyes that absorb in the visible region but fluoresce in the far-red or near-infrared regions are of great interest as labels for biological systems, pigments for light-emitting diodes, sensitisers for organic solar cells and markers on documents or banknotes. Such materials are often photo-labile and suffer from poor solubility. The target compound described herein represents a major step forward in the design of near-IR emitters that are both photo-stable and highly efficient photon collectors. The inefficient quenching of the dye triplet by molecular oxygen is a very rare event, almost unparalleled in the field of organic photophysics.

What has motivated you to conduct this work?

This work is part of a major initiative into the photophysical properties of BODIPY-based dyes - a subject of universal interest around the world. It involves the first combination of a conventional BODIPY dye, absorbing and emitting in the visible region, with an expanded dye that emits at low energy. Successful synthesis of the target compound was made possible by our prior development of suitable protocols for the cross coupling reaction.

Where do you see this work developing in the future?

The next step will involve attaching a range of secondary photon collectors to the network. These will include several different organic chromophores, each possessing a distinctive absorption spectral profile. This will enable a cascade of energy-transfer steps leading to emission in the near-IR region. Prototypic molecules comprising 4 separate light absorbers are already at-hand. Our intention is to further functionalise these prototypes by adding the expanded BODIPY as the ultimate acceptor. Such networks, containing as many as 10 separate chromophores in a single entity, should function as unique markers for anti-forgery systems.

Are there any particular challenges facing future research in this area?

There are many challenges associated with the synthesis and characterisation of such materials. Unravelling the photophysical processes, especially the mechanism for intramolecular electronic energy transfer on sub-ns time scales, is a particular problem that will require a considerable investment in terms of experimental technique and data analysis.