By coupling surface-enhanced Raman spectroscopy (SERS) with thin layer chromatography (TLC), a facile and powerful method was developed for on-site monitoring the process of chemical reactions. Samples were preseparated on a TLC plate following a common TLC procedure, and then determined by SERS after fabricating a large-area, uniform SERS substrate on the TLC plate by spraying gold nanoparticles (AuNPs). Reproducible and strong SERS signals were obtained with substrates prepared by spraying 42-nm AuNPs at a density of 5.54 × 1010 N/cm2 on the TLC plate. The capacity of this TLC-SERS method was evaluated by monitoring a typical Suzuki coupling reaction of phenylboronic acid and 2-bromopyridine as a model. Results showed that this proposed method is able to identify reaction product that is invisible to the naked eye, and distinguish the reactant 2-bromopyridine and product 2-phenylpyridine, which showed almost the same retention factors (Rf). Under the optimized conditions, the peak area of the characteristic Raman band (755 cm–1) of the product 2-phenylpyridine showed a good linear correlation with concentration in the range of 2–200 mg/L (R2 = 0.9741), the estimated detection limit (1 mg/L 2-phenylpyridine) is much lower than the concentration of the chemicals in the common organic synthesis reaction system, and the product yield determined by the proposed TLC-SERS method agreed very well with that by UPLC-MS/MS. In addition, a new byproduct in the reaction system was found and identified through continuous Raman detection from the point of sample to the solvent front. This facile TLC-SERS method is quick, easy to handle, low-cost, sensitive, and can be exploited in on-site monitoring the processes of chemical reactions, as well as environmental and biological processes.
Naphthalenediimide (NDI) was connected to the ligand of a cyclometalated Ir(III) complex (Ir-1) via a CC triple bond to enhance the absorption in the visible region and to access long-lived triplet excited states. Ir(ppy)2(bpy)[PF6] (Ir-2, ppy = 2-phenylpyridine and bpy = 2,2′-bipyridine) was used as a model complex. The photophysical properties of the complexes were studied with steady state and time-resolved spectroscopy. Ir-1 shows strong absorption in the visible region (ε = 11 000 M−1 cm−1 at 542 nm) and in comparison Ir-2 shows typically weak absorption in the visible region (ε < 3000 M−1 cm−1 above 400 nm). Room temperature near IR emission at 732 nm (ΦP = 0.1%) was observed for Ir-1, which is attributed to the NDI localized emissive triplet excited state, by transient absorption spectra and DFT calculations on the spin density surface. The lifetime of the NDI-localized triplet excited state is up to 130.0 μs, which is rarely reported for Ir(III) complexes. In comparison, Ir-2 shows phosphorescence at 578 nm and the triplet state lifetime is a typical value of 0.3 μs. The complexes were used as triplet photosensitizers for triplet–triplet annihilation (TTA) upconversion and an upconversion quantum yield of 6.7% was observed with Ir-1. No upconversion was observed with Ir-2 as the triplet photosensitizer at the same experimental conditions.
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