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A film of [N,N‘-bis(3,5-di-tert-butylsalicylidene)-1,2-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 S,S-1 film on CdSe gives larger PL enhancements and equilibrium binding constants (estimated using the Langmuir adsorption isotherm model) for S,S,-PPO, R,S-PPO, and R-StO than for the enantiomer of each of these epoxides. When the R,R-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 103 to 104 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 Å. The PL response can in principle serve as the basis for an on-line chemical sensor for chiral analytes.

The adsorption of DNA basessadenine (A), thymine (T), guanine (G), and cytosine (C)sand base pairs onto single-crystal n-CdSe substrates has been studied in several solvents, using the band gap photoluminescence (PL) of the semiconductor as a probe. In methanol solution, all four bases cause similar, reversible PL quenching, consistent with their acting as Lewis acids toward the surface. The PL changes can be well fit by a dead-layer model, indicating that adsorption increases the depletion width of the semiconductor by ∼200-300 Å. In DMSO solution, there is no PL response to individual bases. However, the complementary A-T and G-C base pairs yield a PL response, providing evidence that the surface can promote base pair formation. The A-T and C-G responses in DMSO correspond to depletion width increases of ∼100 and 200 Å and persist to ∼45 and 75 °C, respectively. Competition experiments reveal a preference for C-G binding at elevated temperatures. In chloroform solution, the PL response of C-G base pairs can be distinguished from those of C and G individually, whereas A, T, and A-T are experimentally indistinguishable. Electronic and hydrogen-bonding effects that may contribute to the PL responses are discussed.

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