Thanks for your answer Simon. I won't go into too much detail, but I want to observe a shift in the fluorescence peak when my nitrobenzene:decane mixture changes from ~1:1 to ~10:1. Nitrobenzene is very convenient to use for several reasons, but it seems to quench every dye on the face of the earth! Thanks for your help anyway.

Dear Finlay,

your question is too vague and " slightly BAD " formulated. Why ?

Your wished dye must be soluble in nitrobenzene  and decane for a correct UV-Vis measurement   prior to fluorescence measurements.

You can see the solvatochromic properties in this case proir to see a fluorescence shift.

Nitrobenzene is slight yellow  when impure and colorless (pure)and you will have another cut-off  value  than for the decane.

The 2 solvents must  be pure and dry.

have you read the following article posted on R.G.  :

-Fluorescence Quenching Reaction of Porphyrins in Micelles: Ionic Porphyrins Quenched by Nitrobenzene in Ionic Micelles

ARTICLE in JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A CHEMISTRY 174(2):113-118 · AUGUST 2005 with 3 READS

and

Abstract

The spectroscopic and fluorometric properties of nine oxacyanine dyes (3,3'-dimethyloxacarbocyanine through 3,3'-diheptyloxacarbocyanine, 3,3'-diethyl-, and 3,3'-dipropyloxadicarbocyanine iodides) were determined in two solvents, water and nitrobenzene. In nitrobenzene the absorbance and fluorometric spectra of the dyes showed a red shift of 15 to 20 nm when compared with the spectra in water. In addition, the fluorescence emission intensity of the dyes is lower in nitrobenzene than in water, by one to two orders of magnitude. Thus it is possible to measure fluorescence in water in water/nitrobenzene systems without interference from the nitrobenzene part. The molar absorptivities of the dyes were calculated and used to determine the solubility of the dyes in water and the partition coefficients of the dyes between nitrobenzene and water. These dyes were characterized in order to provide a better understanding of the properties of the dyes in a water/nitrobenzene interface system which will be used in electrochemical studies of the dyes.

On other part you must purify your nitrobenezene and decane  prior to an use in the fluorescence spectroscopy.

What a kind of spectrometer  (p.e. Edinburgh Instruments or others)   and cuvettes (quartz ) are you using?

I thimk you are working at room temperature. Note that nitrobenzene is very toxic!!

Your cuvettes must be closed.

JRG

Dear Finley,

Nitrobenzene quenches through an electron transfert from the excited state. You should look for dyes with a low redox potential and low excited state energy. Tetrazine is an example of such a dye by they are not solvatochromics and I have never put them in nitrobenzene.

Hello,

Thank you all for your responses, they were all helpful. I used Methylene Blue since it has a lower quenching constant than other common fluorophores (Page 62, DOI: 10.1016/j.aca.2008.01.016). My goal was to differentiate between nitrobenzene and decane using fluorescence, which is shown in the attached image.