A recent JACS comm (Benedetti et al) has detailed the development of a novel fluorophore, based on cyclopenta[b]naphthalene, and looked into its photophysical properties – namely its solvatochromism and quantum yields. This compound is interesting due to its similarity to the commercially available fluorophore Prodan.
Solvatochromism is a fancy word for the colour change of a species in solutions of different polarity solvents, e.g. unpolar cyclohexane compared to polar methanol. On its own a compounds solvatochromism doesn’t really represent something to write home about as it is fairly predictable (increase polarity, increase red shift). However, it can help one illucidate some fairly fundamental properties about a compound. (I’m going to put a link here to a page I’m writing about solvatochromism – check back soon).
The quantum yield is a very interesting property when photophysically characterising a compound; it represents the ratio of photons absorbed to those emitted, as a percentage. I have to be careful with wording here as the photons absorbed aren’t the ones that are emitted… (follow this link)
Essentially, the quantum yield is a measure of how bright something is. You want this value to be high if you’re designing, for example, a fluorophore.
The JACS communication reports exhaustively on the Prodan-type derivatives.
- In solvents of increasing polarities, the systems uniformly exhibit bathochromic shifts of their emission maxima.
- By placing the electron donating and electron withdrawing substituents gradually further away and in opposite directions, the compound’s Stokes shifts increase.
- Compound 6 (their numbering scheme) exhibits a 300 nm Stokes shift, in ethanol.
- A large Stokes shift which moves the emission into the visible region is very useful for fluorophores being heralded as potential biomarkers/fluorophores.
- Compound 6 displays a quantum yield of 1 % in ethanol…
Seriously. A JACS comm?
E. Benedetti, L.S. Kocsis, K.M. Brummond (2012). Synthesis and Photophysical Properties of a Series of Cyclopenta[b]naphthalene Solvatochromic Fluorophores Journal of the American Chemical Society DOI: 10.1021/ja3055029