A new series of boron complexes consisting of pyridine-pyrazole ligands has been designed, synthesized and evaluated for its Raman activity using solidstate Raman spectroscopy. The detailed surface-enhanced Raman scattering (SERS) study of selected dye 2-(3-(pyridin-4-yl)-1H-pyrazol-5-yl) pyridine (P 4) on gold nanoparticles (AuNPs) of size 40 nm revealed that it can detect as small as the nanomole level with signal quality that is superior to structurally similar commercially available reporter molecules (RMs), rendering it a suitable RM for sensitive SERS nanotags.
This study presents the design and synthetic pathway of unsymmetric ligands based on pyridine-pyrazolate scaffold with Donor–Acceptor (D–A) molecular arrays and their boron complexes to achieve a large Stokes shift. Intermolecular charge transfer (ICT) triggered by the uneven molecular charge distribution from electronically dense pyrazolate (donor) part of the ligands to electron-deficient boron centre (acceptor) resulted in a mega Stokes shift up to 263 nm for selected compounds while retaining the characteristic quantum efficiency and chemical stability. The photophysical properties of derivatization of pyrazolate group in the pyridine-pyrazolate scaffold of diaryl boron complexes were explored based on UV–Visible, steady-state and time-resolved fluorescence spectroscopy. An interesting dual emission along with quenching behaviour was also observed for 2-(6-methoxynaphthelene) 5-(2-pyridyl) pyrazolate boron complex (P5) due to the formation of a twisted intermolecular charge transfer (TICT) state from a locally excited (LE) state rendering it a potential candidate for sensing applications based on H-Bond quenching. In addition, the extended excited state lifetime of the reported compounds compared to classical boron-dipyrromethene (BODIPY) makes them suitable as potential probes for analytical applications requiring a longer excited state lifetime.
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