Charge-transfer complexes of Cu(II)/HD analogue in sol–gel sensors

An optically transparent xerogel encapsulating Cu(II) acetate is fabricated to detect mustard gas (HD) analogues via a charge-transfer mechanism. A fast response (color change from sky blue to canary yellow) is observed for the chlorinated sulfide, and is accompanied by an absorption band at 370–420 nm. MO calculations revealed that the chlorinated HD analogue displays a charge-transfer transition extended from sulfur to chlorine atom. A 1:1 complex of Cu(II)/HD analogue is preferred. For a colorimetric sol–gel detector prepared at pH 3, the detection limit of HD analogue is calibrated at 0.03 μl per 1.5 ml sensor volume.