We have synthesized
the HC^Npz ligand, 1-(naphthalen-2-yl)-1H-pyrazole (1A), and carried out its cyclometalation
reaction with [{Pt(η3-C4H7)(μ-Cl)}2] to give [{Pt(Naph^N)(μ-Cl)}2]. This
process takes place via the intermediate [Pt(η3-C4H7)Cl(HNaph^N-κN)] (2A) which could be isolated and fully characterized. Compound [{Pt(Naph^N)(μ-Cl)}2] and the analogous N-heterocyclic carbene complex [{Pt(Naph^C*)(μ-Cl)}2] (HNaph^C*-κC* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene) were used to prepare the bis-cyanide
anionic derivatives N
n
Bu4[Pt(Naph^E)(CN)2] (E = Npz
4A, C*carbene
4B) which subsequently react with TlPF6 to
afford the corresponding complexes [PtTl(Naph^E)(CN)2] (5A and 5B). The X-ray structures
of 5A and 5B show the presence of 2D extended
networks created by organometallic “PtTl(Naph^E)(CN)2” entities, each one containing a Pt→Tl dative
bond (d Pt–Tl = 3.0205(3) Å 5A, 2.9395(4) Å 5B). These units are linked together
through additional Tl···NC and Tl···π
contacts, which, in the case of 5B, renders a stair-like
arrangement. NBO charge distributions analysis on 4A and 4B shows a small negative charge on the Pt center for 4B, while positive for 4A, indicating the more
electron donating character of the carbene with respect to the pyrazole
group. 195Pt and 13C NMR spectra of N
n
Bu4[Pt(Naph^E)(13CN)2] (E = Npz
4A′, C*carbene
4B′) account for this
difference. Photophysical analysis has been performed for 4A/B and 5A/B regarding the Naph^E fragment. The emissions
of 4A and 4B in CH2Cl2 at 77 K present similar profiles and have been assigned to 3ILCT [π(Naph^E) → π*(Naph^E)] excited states.
The green emission of 4A in poly(methyl methacrylate)
(PMMA) film (5 wt %) affords a photoluminescence quantum yield (PLQY,
Φ) of 82%. In the solid state, the vibronic emissions of 5A (λmax = 528 nm) and 5B (λmax = 561 nm) are red-shifted in relation to their precursors
(λmax = 488 nm 4A, 530 nm 4B) and are mainly attributed to 3MM′LCT [d/s σ*(Pt,Tl)
→ π*(Naph^E)] excited states.