With the help of a photophysical model, scientists in the US have discovered dual fluorescent dyes (where two colours are emitted from the same fluorophore), which could prove useful in detecting clinically important molecules.

Michael Heagy and co-workers from the New Mexico Institute of Mining and Technology synthesised a matrix of nine naphthalimide dyes. They used a seesaw balanced photophysical model to balance the dyes' electronic properties by directing substituent groups on the dyes to the correct positions. Four out of the nine dyes in the matrix showed dual fluorescence.

'Just as green and red traffic signals convey far more information to a motorist than a single yellow caution flasher, so also is the greater information obtained from dyes that emit in two colours to researchers who are attempting to detect a molecule, an ion or another clinically important system,' explains Heagy. 'The ability to obtain two colours from an organic dye improves biological analyses by providing a second signal or output to monitor. This enables better accuracy as the second colour provides internal calibration of the signal.'

Obtaining dual fluorescent dyes has previously proved difficult because of factors such as substituent groups on the molecule and the solvent affecting whether dual fluorescence will occur. Chemists have had to synthesise large libraries of dyes where only a small fraction turn out to be dual fluorescent.

Robert Strongin, who develops new organic reagents used in diagnosing, understanding and treating diseases at Portland State University, US, says, 'It's not often that simple and elegant predictive models for tuning fluorophore photophysics are reported.' He adds that the work of Heagy's group represents 'a breakthrough that will allow better understanding of fluorophore properties, and enable the design of improved optical materials.'

Heagy envisions dual fluorescent naphthalimide dyes being used in chemosensory devices for ion and molecule detection because of their advantages over conventional one-colour dyes.

Fay Nolan-Neylan

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