Depends on the specific hosts and guests of you chemosensors.

Your question is unfortunately a bit too vague to give a definitive answer.

Different possibilities may arise..

(i) Metal ion sensing:

H+ and M+ (metal ions) are two competitive ions for comlex formation with ligands. If pH is low, then the ligand can strongly bind with H+ instead of M+. It is also to be mentioned that the binding mode of H+ and M+ will be different, resulting different optical signal. This signal may merge with the optical response of other metal ions and consequently, one can not discriminate between the metal ions. On the other hand, high pH may cause precipitaion of metal hydroxide. So it is necessary to test the sensitivity of the ligand upto which the sensing mechanism is independent of pH. Buffer solution will be effective to balance the sensing mechanism.

(ii) Anion sensing:

pH also effects the anion sensing. In low pH, target anion may bind with H+ instead of ligand and in high pH, there will be competition between target anion and OH-. So neutral pH will give the better picture.

(iii) Neutral molecule sensing:

If a sensor or guest contains lone pair and Y-H bond (Y=F,O,N), then pH may effect the sensing equilibrium. There may form bonding between lone pair and H+ at low pH whereas at higher pH, hydroxide may take the protons from the ligands at high pH, keeping aside the guest molecule.

Best of luck,

Atanu

Dear Bhriguram, can you reformulate your quetion?

Regards

Hi, Dear Rosa, we synthesized a Schiff base chemosensor for Zn2+. the probe have a =NH- and -OH group. One of the reviewer just asked "How does the pH affect sensing equilibria ?"

So, you have been ask to perform pH dependent experiments. Quite reasonable question from rev., since the metal-ligand intteractions are strongly affected by the acid/base equilibria... especially when the coord. atoms itself may act as a acid/base centres (as in your case).

Make those experiments and you will answer yourself and the reviewer.