Synthesis and photophysical investigations of pyridine-pyrazolate bound boron(III) diaryl complexes.

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.

N-Cyclo-hexyl-benzamide.

The structure of the title compound, C(13)H(17)NO, features an anti disposition of the N-H and carbonyl groups. The amide group is twisted with respect to the benzene ring [N-C(=O)-C-C torsion angle = -30.8 (4)°]. In the crystal, C(4) chains propagating in [100] are formed by inter-molecular N-H⋯O hydrogen bonds. Weak C-H⋯π inter-actions link the chains into sheets.

Methyl 2-(4-chloro-benzamido)-benzoate.

In the title compound, C(15)H(12)ClNO(3), the central C-C(O)-N-C amide unit makes dihedral angles of 6.60 (2) and 3.42 (2)°, respectively, with the 4-chloro-benzene and anilino rings. The dihedral angle between the two benzene rings is 3.32 (3)°. Intra-molecular N-H⋯O and C-H⋯O hydrogen bonds form S(6) rings and contribute to the planarity of this portion of the mol-ecule. In the crystal, inter-molecular C-H⋯O hydrogen bonds are observed, which link the mol-ecules into [010] C(7) chains.