B-N coordinated triaryl pyrazole: effect of dimerization, and optical and NLO properties

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2019, Vol.7 (4), p.12725-12737
• Main Authors: Mukundam, Vanga, Sa, Shreenibasa, Kumari, Anupa, Das, Ritwick, Venkatasubbaiah, Krishnan
• Format: Article
• Language: English
• Subjects: Absorptivity; Benzene; Carbazoles; Conjugation; Crystallography; Dichloromethane; Dimerization; Dimers; Dipole moments; Optical properties; Pyrazole; Synthesis; X ray analysis
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c9tc04309h

A series of triaryl pyrazole B ← N coordinate dimers with different π-conjugated (spacer) bridges (compound 4 (no spacer); compound 7 (2,5-bis(hexyloxy)benzene); compound 8 (9,9-dihexyl-9 H -fluorene); compound 9 (9-hexyl-9 H -carbazole); compound 10 (thiophene); compound 11 (2,2′-bithiophene)) has been synthesized from simple triaryl pyrazoles. Three different synthetic protocols were applied to synthesize the desired B ← N coordinate pyrazole dimers. All the B ← N coordinate pyrazole dimers exhibit absorption maxima between 337 and 399 nm with good molar absorption coefficients (12 000 to 22 100 M −1 cm −1 in CH 2 Cl 2 ). They are highly emissive in the solution state with quantum yields of up to 0.94. Due to a substantial change in the excited state dipole moment, B ← N coordinate pyrazole dimers exhibit versatile and appreciably large nonlinear optical (NLO) properties. The dimer symmetry and the presence of donor or acceptor moieties affect the two-photon-absorption (TPA) cross-section substantially. In addition, the investigation reveals that the dimer π-conjugation length in all dimer variants has a remarkable impact on the NLO characteristics. Triaryl pyrazole B-N coordinate dimers with and without π-conjugation exhibit unique photophysical (linear as well as nonlinear optical) properties.