Tuning the Fluorescence Emission and HOMO‐LUMO Band Gap in Homoleptic Zinc(II) Complexes with N,O‐Bidentate (Imidazo[1,5‐a]pyrid‐3‐yl)phenols

• Published in: European journal of inorganic chemistry Vol. 2019; no. 13; pp. 1825 - 1831
• Main Authors: Ardizzoia, G. Attilio, Colombo, Gioele, Therrien, Bruno, Brenna, Stefano
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 09.04.2019; Wiley Subscription Services, Inc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Crystal structure; Density functional calculations; Dichloromethane; Emission analysis; Energy gap; Fluorescence; Inorganic chemistry; Luminous intensity; Molecular orbitals; N ligands; Nitrogen dioxide; Phenols; Photochemistry; Photoluminescence; Physical Sciences; Science & Technology; Structural analysis; Ultraviolet radiation; Zinc; Zinc compounds; COPPER(I); TRANSITION-METAL-COMPLEXES; BLUE; ZN(II); Fluorescence; Density functional calculations; LUMINESCENT PROPERTIES; SUPRAMOLECULAR STRUCTURES; X-RAY CHARACTERIZATION; Zinc; N ligands; SENSITIZED SOLAR-CELLS; LIGAND; CATALYTIC-ACTIVITY; Photochemistry
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201900067

A series of homoleptic zinc(II) complexes of the general formula [Zn(LR)2] (HLR: (imidazo[1,5‐a]pyrid‐3‐yl)phenol; R: para‐substituent to the phenol) have been synthesized. The single‐crystal X‐ray structure analysis of complex [Zn(LH)2] (1) confirmed the expected N,O‐bidentate coordination of LR, via the pyridine‐like nitrogen of the imidazo[1,5‐a]pyridine skeleton and the phenolate oxygen. The photophysical properties of the complexes have been investigated in dichloromethane solution, showing fluorescence emission when excited with UV light (λexc = 340–360 nm). The intensity and λmax of the emission are both significantly influenced by the R‐substituent, the emission maxima moving from blue (R = CF3, Zn(LCF3)2] (6)) to orange (R = NO2, Zn(LNO2)2] (7). Most of [Zn(LR)2] compounds are characterized by moderate‐to‐good absolute photoluminescence quantum yields, with a maximum of 0.33 for [Zn(LH)2] (1). Density functional calculations allowed to identify the Natural Transition Orbitals involved in the electronic transitions and define the main transition as being HOMO‐LUMO (>95 %) in character. A good linear correlation was found between the HOMO energy and the Hammett σp constants associated to the R‐substituent, whereas the fluorescence behavior has been described in terms of HOMO‐LUMO band gap. A series of homoleptic zinc(II) complexes with N,O‐imidazo‐pyridine ligands is presented. They show an intense fluorescence emission in solution, with high Stokes shifts and quantum yields. Besides, λmax is tunable by the electronic features of the substituent R at the para position of the bound‐to‐zinc hydroxyl group.