BORAZANs:  Tunable Fluorophores Based on 2-(Pyrazolyl)aniline Chelates of Diphenylboron

Authors

Brendan J. Liddle, Marquette University
Rosalice M. Silva, Marquette University
Tyler James Morin, Marquette University
Felipe P. Macedo, Marquette University
Ruchi Shukla, Marquette University
Sergey V. Lindeman, Marquette UniversityFollow
James R. Gardinier, Marquette UniversityFollow

Document Type

Article

Language

eng

Publication Date

2007

Publisher

American Chemical Society

Source Publication

The Journal of Organic Chemistry

Source ISSN

0022-3263

Abstract

The reaction between 2-pyrazolyl-4-X-anilines, H(pzAn^X), (X = para-OMe (L1), Me (L2), H (L3), Cl (L4), CO₂Et (L5), CF₃ (L6), CN (L7)) and triphenylboron in boiling toluene affords the respective, highly emissive N,N‘-boron chelate complexes, BPh₂(pzAn^X) (X = para-OMe (1), Me (2), H (3), Cl (4), CO₂Et (5), CF₃ (6), CN (7)) in high yield. The structural, electrochemical, and photophysical properties of the new boron complexes can be fine-tuned by varying the electron-withdrawing or -donating power of the para-aniline substituent (delineated by the substituent's Hammett parameter). Those complexes with electron-withdrawing para-aniline substituents such as CO₂Et (5), CF₃ (6), and CN (7) have more planar chelate rings, more ‘quinoidal' disortion [sic] in the aniline rings, greater chemical stability, higher oxidation potentials, and more intense (φ_F = 0.81 for 7 in toluene), higher-energy (blue) fluorescent emission compared to those with electron-donating substituents. Thus, for 1 the oxidation potential is 0.53 V versus Ag/AgCl (compared to 1.12 V for 7), and the emission is tuned to the yellow-green but at an expense in terms of lower quantum yields (φ_F = 0.07 for 1 in toluene) and increased chemical reactivity. Density functional calculations (B3LYP/6-31G*) on PM3 energy-minimized structures of the ligands and boron complexes reproduced experimentally observed data and trends and provided further insight into the nature of the electronic transitions.

Comments

Accepted version. The Journal of Organic Chemistry, Vol. 72, No. 15 (2007): 5637-5646. DOI. © 2007 American Chemical Society. Used with permission.

Recommended Citation

Liddle, Brendan J.; Silva, Rosalice M.; Morin, Tyler James; Macedo, Felipe P.; Shukla, Ruchi; Lindeman, Sergey V.; and Gardinier, James R., "BORAZANs:  Tunable Fluorophores Based on 2-(Pyrazolyl)aniline Chelates of Diphenylboron" (2007). Chemistry Faculty Research and Publications. 629.
https://epublications.marquette.edu/chem_fac/629