Your question is too vague. Please give us Infos about your solvent and give us a picture of your reactor vessel. Are you using glass or quartz.

Are you using a support for the irradiation?

When dealkylation of Rhod B occurs , it is better to do a TLC (Thin layer Chromatogramm) because the change with UV-Vis are very small.

If you have amino group after the dealkylation, you can observe the change.

JRG

I send you 2 spectra (RhodB and Rhod 110. you can see the difference in methanol.

Absorption max Rhod B 545 nm

" " Rhod 110 498 nm

I measured the spectra of Rhod B salt in water four decades ago:

absorption max 554 nm and the tri-ethyl Rhodamin (1 ethyl group lost) was 553 nm.

Are you using blue LED (e.g. UV LED) for your investigation? If you see no changes (per TLC) perhaps are 50 W too weak for your irradiation.

JRG

Thank you sir for your reply.

Sir i have prepared 0.01mM solution of RhB in water as a solvent to which i added 500 mg of my compound and stirred for 2 hours in dark and under constant stirring irradiated with 50 W LED from top at a distance of 10 cm and afetr every 1 hour it took 5 ml of sample centrifuged it for 30 minutes at 5000 rpm and took uv-vis. this i did for 8 hours but i didnot observe any change in uv-vis.sir i have attach my experimental set up please kindly guide me on my set up and any improvisation i can make with it.

Thank you for the fast reply and for the picture.

Please reread my previous answer (Kind of LED/White LED or Blue LED?)

If your "compound" e.g. the structure is confidential, you can send me the name via message (only you and JRG can see the sentences).

According to the picture, It seems that you use a white light LED and you have a suspension. On other part, according to my previous answer, try to obtain a blue LED (50W for the reproducibility) . Than you can see the strong fluorescence of Rhod B in water. You can see the dealkylation and the loss of 4 ethyl groups only with TLC.

JRG

Dear sir thank you for the reply.Sir you have recommended for TLC but in all the papers i have come across in photo catalysis i didn't find TLC being done rather UV-Vis absorbance study is carried out.Sir could you please refer me to some paper where they have done TLC .Due to think i should use 300 W LED for my study.

According to my messages and your answers, I think you are right when you write :

I tried with rhodamine B with irradiation source 50 W LED but could not observe any change in the UV-Vis spectrum for the sample taken out after interval of 1 hour each. even for sample irradiated for 8 hours there was no change.my question is is there problem with my irradiation source……..

I think it is a problem with your irradiation source (50 W or 300 W) (see above /question/ answer). Why?

If you use a commercial 300W LED, you have a complex light mixture (e.g. IR and UV) because this kind of source are for plant growth and not for photocatalysis research!

In my answer (7 days ago) I wrote try with UV blue LED.

Can you buy this UV LED?

According to your picture, the distance between the source and the surface of the water is too big!

My advice in your case:

Please read my joined files:

file:///C:/Users/jeang/Downloads/yao2012.pdf

file:///C:/Users/jeang/Downloads/yang2005.pdf

In reference Yang et al. 2005, the authors describe the irradiation reactor used for rhodamine B and MB salts.

if you are not familiar with the degradation of MB salt, I joint the picture taken from Yang et al. (page 210)(you can see MB/Dealkylation/Scission/…)

I think that you must use such a reactor (with cooling) for your experiment.

Concerning your compound :

You write:

i wanted to study the photocatalytic property of a compound whose band gap is around 1.7 eV..

Are you using CdSe? CdSe value is 1,74 eV.

Concerning my answer about TLC. It is an old analytical method for "small budget scientist" without MS possibilities!

P.e. your experiment was successful!. You have a water solution with the suspension of your compound. After filtration, your filtrate is clear.

You can extract the degradation products as follows:

you take a separatory funnel and give an amount of CH2Cl2 to the water solution for the extraction. In your CH2Cl2 solution you ´ll have the aromatic amines and traces of MB or Rhod B (if the degradation was not complete) and another compounds.

With TLC you can see (with an UV lamp) various spots.

If you don ´t know anything about TLC , consult please your supervisor.

Well, good luck

JRG