Detection of Chiral Analytes through Adduct Formation with Chiral Films Coated onto Emissive Cadmium Selenide Substrates

摘要

A film of [N,N'-bis(3,5-di-tert-butylsalicylidene)-l,2-cyclohexanediamine]manganese(III) chloride, 1, adsorbed onto an n-type CdSe single-crystal substrate acts as a stereoselective transducer for chiral analytes, coupling the complexation chemistry of the film to the band gap photoluminescence (PL) intensity of the underlying semiconductor. Exposure of the uncoated semiconductor to phenylpropylene oxide (PPO) and styrene oxide (StO) vapor results in a small PL enhancement relative to a vacuum reference level that is the same within experimental error for the four PPO and for the two StO stereoisomers. In contrast, exposure of the coated semiconductor to PPO and StO vapor substantially enhances the CdSe PL intensity relative to its intensity under vacuum conditions, and the optical response is stereoselective, with the PL enhancements and equilibrium adsorption constants dependent on the chirality of both the adsorbate and film. Use of a 5,5-1 film on CdSe gives larger PL enhancements and equilibrium binding constants (estimated using the Langmuir adsorption isotherm model) for 5,5,-PPO, R,S-PPO, and R-StO than for the enantiomer of each of these epoxides. When the RJR-1 film is employed on CdSe, the expected enantiomeric relationship is observed,with R,R-PPO, S,R-PPO, and S-StO yielding larger PL enhancements and equilibrium binding constants. Binding constants for the preferred film-analyte interactions are in the range of 10~3 to 10~4 atm~(-1). The PL enhancements can be fit to a dead-layer model, except at short wavelengths where evidence for photodissociation of the epoxide from the film is obtained, and maximum reductions in depletion width caused by epoxide--film adduct formation are estimated to range from ~200 to 800 A. The PL response can in principle serve as the basis for an on-line chemical sensor for chiral analytes.