Synthesis of luminescent BPh2-coordinated 2-(2′-hydroxyphenyl)benzoxazole (HBO)

Abstract

Triphenylborane (BPh3) has been successfully coordinated to five π-conjugated aromatic systems containing a N∧O bidentate 2-(2′-hydroxyphenyl)benzoxazole (HBO) ligand. Complexes 6–8 are directly substituted on the phenolic side of the HBO core while the structure of derivatives 9–10 includes a 4-dibutylaminophenyl module linked through an ethynyl fragment, at position 4 or 5. The crystal structure of complexes 8 and 10 reveals different solid-state molecular packing depending on the substitution, a herringbone molecular packing being observed for complex 8 while the dibutylamino fragment present in complex 10 is in favour of a lamellar structure. The optical properties are highly dependent on the nature and the position of substituents. Solvatochromic charge-transfer emissions are observed for substitution at position 3 or 5 while singlet emission is favoured when position 4 is functionalized. Solid-state fluorescence reveals that complex 8 possesses red-shifted emission when dispersed in a KBr matrix.