DMF has high absorbtion bellow 268 nm, so it cannot be used. Methanol, on the other hand, is ok to as low as 205 nm. Absence of one peak in different batch of the compound suggest that peak comes from some contaminant (perhaps in the UV cuvette), shifting of abs. maxima by few nm can happen in different solvent.

The discontinuity in your spectrum could be due to diffraction grating change in the spectrophotometer. The spectrophotometer uses different gratings for different wavelength ranges, and the grating change can slightly shift the incident beam direction. If your sample is not completely filling the entire excitation window, the beam can be repositioned to a location with slightly more/less reflection losses, creating a sharp offset like that observed in the peak of your spectrum. Ensure by inspection that there is not an air gap at the top of the sample that is visible through the excitation window.

I agree with Jiri Koubek, this could be a plausible reason. How about decreasing the concentration? Abs of 3 seems a bit high. I'm not very sure but, some information may come out of it if there is an aggregation issue. You could even try a mixed solvent effect (varying DMF/MeOH ratio) to see at what point the scrambling is lost/appears. Try a range of solvents like aprotic, protic, polar protic to check if the observations a consistent for a particular nature of the solvent. I would suggest these are worth a try.

Good luck !

I always use ACN for my masurements as it is transparent up to 190nm.Check the solubility of your compound in ACN. If it is aggregation, you would see the bands go crazy, not just scrambling but a steady increase and tailing of the bands. You should always do a blank everytime before you run any sample. For example use just DMF or methanol and check its UV-vis. It is possible that your solvents are not good anymore. Good luck!

thank you all, my compound is not soluble in ACN. i will try your suggestions

I agree with the answers of Jiri, Geoffrey,Rupashree, Subramani . But please note:

- NMR purity is not good enough.

At first , you need an elemental analysis of your drug . The "found" values must be + / - 0,1-0,2 % related to the calculated values. Before you give your drug for elemental analysis, you must dry it in vacuum (presence of water or solvent acquired during the synthesis) until the elemental values remain constant.

When you dissolve your drug in a pure spectroscopical solvent for UV-Vis, your solvent must be dry and fresh distillated.

UV/Vis solvents have a CUT OFF value (see above)

UV cut-off

(nm,

T1cm

thank u for your kind answer sir. we have a single beam spectrometer. i will submit the sample for ESI-MS

Dear Rathna,

did you check whether your spectrometer switches between the UV and the VIS light source (e.g. deuterium vs. wolfram or halogen) at or around 320 nm? This can lead to the artificial peak at 320 nm.

I have a lot of questions again and agree with the above researchers concerning the spectrometer and UV-Vis sources.

Questions:

-How old is the spectrometer? (Cy , maintenance concerning the UV-Vis sources/I know, they are expensive.

- Glass or quartz cells? You know that the glass cells must be used for spectra between 320 nm (cut off) to 2500nm . You can read OS on the cells (OS = optic special glass). Green mark can be seen

-Quartz cells Suprasil (QS can be read). 200 nm to 2500nm. QS cells have a blue mark.

-Quartz cells Suprasil (QI can be read). The mark is red.

PLEASE NOTE THAT :

- the cell must be closed (Teflon) . With open cell (The cell cavity is warm) , the solvent can evaporate and you have another concentration (c) during the obtention of the spectrum.

The cell be filled to the middle and above the slit.

With your single beam spectrometer, you must, at first and with the right cell (see above), measure and store the pure spectroscopical solvent. With another cell (same quality), you solve, filtrate your product and measure the spectrum of your product.

The following product spectrum will be corrected with the stored spectrum of your solvent.

PLEASE NEVER GIVE YOUR CELLS to a colleague . An adsorbed product can be present, even if the fellow say: " I washed them wirh water, ethanol or acetone".

The E value of your measured drug must be always under 2.

You write (in your question):

the fact underlying behind the 320 and the 327nm peak. my compound is symmetric. can anyone explain these observations?

What do you mean with : SYMMETRIC

A drug can be symmetric like diphenyl or diphenyl ethan e.g. methan or or other annelated aromatic ring.

Without steric hindrance , your spectrum must be quite twice of the single part.

With steric hindrance, you´ll obtain a different spectrum.

P.e. the spectrum of diphenylethan is identical with toluol (ca. twice), the spectrum of diphenylmethan is very slight different.

The spectrum of diphenyl ist different because the rings are conjugated and a strong K band can be seen.

Thank you in advance for your answer. good luck

JRG

.

thank you lehmann and jean.

The spectrometer is 10yrs old and the lamp is 2yrs old. If the problem is with the spectrometer, then all the spectra's recorded in that range, in that instrument should have this problem but which is not so.

we are using quartz cuvettes I have recorded good spectras using this cuvettes for several compounds.

I'm using DMF as the solvent which is less-volatile. so the evaporation of the solvent wont be a problem. Even for a low concentrarion like 10*-6 the absorbance comes around 3. why is it so? do the compound has high e value?

my compound has a plane of symmetry. The compound has two -NH groups Do the H-bonding of the drug with the solvent induce the above observed spectra? To clear this doubt, i thought of recording the spectra in a aprotic solvent but the drug is soluble only in DMF.

My research is based on the photophysical measurements of some new complexes. but the ligand itself giving these problems.I'm confused whether i can continue with this drug or not. please help me to sort out this.

note: the XRD contains the solvent coordinated to the drug through the NH group

Dear Rathna,

thank you for your answer and infos. However, experts and I can only help as follows:

- the kind of ligand is needed ( I don ´t need the exact formula of your ligand) but I must know wether it is a Bodipy, tetraphenylporphyrine, phtalocyanine, dipyridil or another kind with nitrogen as ligand.

What a metall will be used in your research Mg, Co, Ni,Zn....).

Please note that your DMF for spectrometry purpose must be colourless and smellless and fresh destillated too.

Can you write more about your X-Ray-Diffraction results (Ligand/DMF)?

Have you taken spectra of your ligand with metals (UV-Vis, ....) ?. Have you seen luminescence in DMF?

JRG

sorry sir for my late reply, my compound contains dipyridine and i thought of using Cu, Co, Ru, Fe, Ni, whichever is working. The DMF solution of the crude compound was pink in colour and the peak appears around 513nm. But after purification, no such colouration

As you can see, it is always difficult to answer a question with few infos (see your question).

Recommendation:

When you write :

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

The absorption spectrum of my compound has two peaks, 320nm and 327nm

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

It is better to write : the absorption of my compound (FREE Form or Metall FREE) has ......

Another hint:

Well, thank you for your answer and infos.

If you use 2,2´-dipyridine or 4,4´-dipyridine, you´ll have different kinds of metallation (chelatation, coordination...). On other part, if you have substituents (e.g. alkyl chains...) on your pyridine part (e.g. monosubstitued or di-substitued) , one will be out of the plane. The study of the metallation /Demetallation will give you interesting results for spectral studies too. You must be sure that the metallated compound give ONLY ONE specie in the solvent prior to measure or take your UV-Vis spectrum, e.g. that NO Demetallation in any extent occurs.

Good luck

JRG