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. Issue 13 (6th March 2019)

• Record Type: Journal Article
• Authors: Ardizzoia, G. Attilio; Colombo, Gioele; Therrien, Bruno; Brenna, Stefano
• Is Part Of: European journal of inorganic chemistry. Issue 13(2019)
• Page Start: 1825
• Page End: 1831
• Publication Date: 2019-03-06
• Subjects: Fluorescence -- N ligands -- Density functional calculations -- Zinc -- Photochemistry; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201900067
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : A series of homoleptic zinc(II) complexes of the general formula [Zn(L R )2 ] (HL R : (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(L H )2 ] (1 ) confirmed the expected N, O ‐bidentate coordination of L R, 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 λ max of the emission are both significantly influenced by the R‐substituent, the emission maxima moving from blue (R = CF3, Zn(L CF3 )2 ] (6 )) to orange (R = NO2, Zn(L NO2 )2 ] (7 ). Most of [Zn(L R )2 ] compounds are characterized by moderate‐to‐good absolute photoluminescence quantum yields, with a maximum of 0.33 for [Zn(L H )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. Abstract : 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, λ max is tunable by the electronic features of the substituent R at the para position of the bound‐to‐zinc hydroxyl group.