Surface-enhanced Raman spectroscopy (SERS) has long been considered as a noninvasive technique that can obtain the fingerprint vibrational information of surface species. We demonstrated in this paper that a laser with a power level considered to be low in the traditional SERS measurement can already lead to a significant surface reaction. para-Aminothiophenol, an important probe molecule in SERS, was found to be oxidized to form 4,4'-dimercaptoazobenzene (DMAB) on a roughened silver surface during the SERS measurement. The assumption was confirmed experimentally by surface mass spectroscopy and SERS as well as electrochemistry of the synthesized DMAB, which agrees well with theoretical calculations. A defocusing method was used to avoid the laser induced surface reaction and perform reliable SERS characterization and identification, which can effectively avoid erroneous interpretation of the distorted experimental result.

p-aminothiophenol (PATP) is an important molecule for surface-enhanced Raman spectroscopy (SERS). It can strongly interact with metallic SERS substrates and produce very strong SERS signals. It is a molecule that has often been used for mechanistic studies of the SERS mechanism as the photon-driven charge transfer (CT) mechanism is believed to be present for this molecule. Recently, a hot debate over the SERS behavior of PATP was triggered by our finding that PATP can be oxidatively transformed into 4,4'-dimercaptoazobenzene (DMAB), which gives a SERS spectra of so-called "b2 modes". In this perspective, we will give a general overview of the SERS mechanism and the current status of SERS studies on PATP. We will then demonstrate with our experimental and theoretical evidence that it is DMAB which contributes to the characteristic SERS behavior in the SERS spectra of PATP and analyze some important experimental phenomena in the framework of the surface reaction instead of the contribution "b2 modes". We will then point out the existing challenges of the present system. A clear understanding of the reaction mechanism for nitrobenzene or aromatic benzene will be important to not only understand the SERS mechanism but to also provide an economic way of producing azo dyes with a very high selectivity and conversion rate.

The cyclic alkyl(amino) carbene (cAAC:)-stabilized acyclic germylones (Me2-cAAC:)2Ge (1) and (Cy2-cAAC:)2Ge (2) were prepared utilizing a one-pot synthesis of GeCl2(dioxane), cAAC:, and KC8 in a 1:2:2.1 molar ratio. Dark green crystals of compounds 1 and 2 were produced in 75 and 70% yields, respectively. The reported methods for the preparation of the corresponding silicon compounds turned out to be not applicable in the case of germanium. The single-crystal X-ray structures of 1 and 2 feature the C-Ge-C bent backbone, which possesses a three-center two-electron π-bond system. Compounds 1 and 2 are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds 1 and 2 confirmed the singlet spin ground state. DFT calculations on 1/2 revealed that the singlet ground state is more stable by ~16 to 18 kcal mol(-1) than that of the triplet state. First and second proton affinity values were theoretically calculated to be of 265.8 (1)/267.1 (2) and 180.4 (1)/183.8 (2) kcal mol(-1), respectively. Further calculations, which were performed at different levels suggest a singlet diradicaloid character of 1 and 2. The TD-DFT calculations exhibit an absorption band at ~655 nm in n-hexane solution that originates from the diradicaloid character of germylones 1 and 2.

The chemistry of white phosphorus has generated much interest over the past decades owing to its unique tetrahedral structure and variable bonding situation. Organophosphorus compounds can be used as reagents [1] and as ligands for innumerable complexes in catalytic processes.[2] The reactions of transition-metal complexes with white phosphorus have been extensively studied and have resulted in a large variety of P x ligands with unpredictable structures.[3] Among them, only one compound [Cp* 2 (CO) 2 Co 2 P 4 ] (Cp* = C 5 Me 5 ) [4] with a {P 4 } 4À species is reported. However, the reactions of the P 4 molecule with main-group complexes are limited to a few examples, [(AlCp*) 6 P 4 ], [5a] [(GaR) 3 P 4 ] (R= (SiMe 3 ) 3 C), [5b] and [Ga 2 P 4 tBu 6 ].[5c][LAl I ] (1) (L = HC(CMeNAr) 2 , Ar = 2,6-iPr 2 C 6 H 3 ) [6] with its nonbonding lone pair of electrons at aluminum indicates a singlet carbene-like character. It could be used in carbenetype reactions, as a Lewis base and moreover as a reducing reagent, which may show unprecedented chemical reactions. To our knowledge, the study of the chemical behavior of 1 is limited so far to coupling reactions. [7,8] Compounds containing the heavy elements of Group 13 and 15 are used as models in bonding theory [9] and as precursors for semiconducting materials.[10] Herein we report the reaction of 1 with white phosphorus to yield the first main-group complex of composition [(LAl) 2 P 4 ] (2) containing the {P 4 } 4À species. Treatment of two equivalents of 1 with white phosphorus at room temperature leads to 2 in good yield (Scheme 1). In contrast, the reaction of the tetrahedral aluminum(i) compound [(AlCp*) 4 ] with white phosphorus gave the electrondeficient cage compound [(AlCp*) 6 P 4 ], [5a] which consists of two face-sharing heterocubanes with two opposing corners unoccupied, and four P atoms from the complete cleavage of the P 4 molecule. Therefore we treated 1 with P 4 in a 4:1 ratio to explore the possibility of complete cleavage of all P À P bonds, however we obtained 2 and residual 1, based on the results of 1 H and 31 P NMR spectroscopic investigations. Clearly the bulky ligand L prevents the arrangement of a larger number of LAl moieties around the P atoms. When the reaction was carried out in a ratio of 1:1 between 1 and P 4 , 2 and residual P 4 together with some byproducts were obtained, again based on the results of 1 H and 31 P NMR spectroscopic investigations. Compound 2 is air sensitive and decomposes at 145 8C. 2 is sparingly soluble in pentane and hexane, however readily soluble in benzene, toluene, and diethyl ether. In CDCl 3 we observed the decomposition of 2.Compound 2 was characterized by 1 H, 13 C, and 31 P NMR spectroscopy using [D 6 ]benzene as the solvent, and by EI mass spectrometry and elemental analysis. The EI mass spectrum shows the molecular ion of 2. The 31 P NMR spectrum of 2 (d = 78.6 ppm) has a very different chemical shift compared to that of the free P 4 molecule (d = À519 ppm). No resonance signals were observed in C 6 D...

A neutral C4 cumulene 1 that includes a cyclic alkyl(amino) carbene (cAAC), its air-stable radical cation 1(·+) , and dication 1(2+) have been synthesized. The redox property of 1(·+) was studied by cyclic voltammetry. EPR and theoretical calculations show that the unpaired electron in 1(·+) is mainly delocalized over the central C4 backbone. The commercially available CBr4 is utilized as a source of dicarbon in the cumulene synthesis.