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

Rashid Javaid; Aziz Ul Rehman; Manan Ahmed; Mohammad Hashemi Karouei; Nima Sayyadi

doi:10.1038/s41598-022-20796-2

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

Sci Rep. 2022 Oct 1;12(1):16482. doi: 10.1038/s41598-022-20796-2.

Authors

Rashid Javaid¹, Aziz Ul Rehman^{2

3}, Manan Ahmed⁴, Mohammad Hashemi Karouei⁵, Nima Sayyadi^{5

2}

Affiliations

¹ Department of Molecular Sciences, Macquarie University, Sydney, NSW, 2109, Australia. rashidjavaid143@gmail.com.
² ARC Centre of Excellence for Nanoscale Bio Photonics (CNBP), Macquarie University, Sydney, NSW, 2109, Australia.
³ Agriculture & Biophotonics Division, National Institute of Lasers and Optronics College, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad, 45650, Pakistan.
⁴ School of Chemistry, The University of New South Wales, Sydney, 2052, Australia.
⁵ Department of Molecular Sciences, Macquarie University, Sydney, NSW, 2109, Australia.

Abstract

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.