4 ′‐ (5 ‐ n ‐ Propylthiophen ‐ 2 ‐ yl) ‐ 2,2 ′ :6 ′ ,2 ″‐ terpyridine

: A new thiophene ‐ substituted terpyridine derivative has been prepared through the reac ‐ tion between 5 ‐ n ‐ propylthiophene ‐ 2 ‐ carboxaldehyde and 2 ‐ acetylpyridine. This terpyridine deriv ‐ ative bears an alkyl chain linked via a thiophene heterocycle.


Introduction
2,2′:6′,2″-Terpyridine (terpy) ligands and their metal complexes have been widely studied [1] owing to the broad range of applications for such molecules. Varying the nature of the substituents on the ligands and/or the metallic centre offers the possibility to prepare an enormous number of different substances. In particular, terpyridines that contain the five membered heterocycle thiophene [2] have attracted widespread of attention. In fact, they can be used in the preparation of materials for solar cells [3][4][5], for the functionalization of nanoparticles [6], as fluorescent probes [7,8], as antimicrobial agents [9], as electrochromic materials [10] or as chromophores [11], just to name a few. The substituents that are present on the thiophene ring have an important impact, especially on properties of thiophene-substituted terpyridine-based materials [12]. Therefore, the preparation of new thiophene-substituted terpyridines is still of interest. This paper presents the synthesis of the novel 4′-(5-n-propylthiophen-2-yl)-2,2′:6′,2″-terpyridine ligand (1) ( Figure  1).
As in many cases with this synthetic protocol, the crude product was sufficiently pure (>98% by quantitative NMR [17,18] and by combustion analysis) to be used (e.g., for the preparation of metal complexes) without purification.
Ligand 1 was characterized by 1 H and 13 C-NMR as well as by HR-MS. Firstly, the 1 H-NMR spectrum agrees with the chemical structure. NMR spectra of 4′-functionalized terpyridines exhibit a typical singlet for proton 3′ and 5′. In the present molecule, this singlet is seen at δ = 8.63 ppm. Furthermore, as expected, hydrogens that belong to the thiophene heterocycle (a and b) appear as doublets centered at 7.60 and 6.84 ppm, respectively, with a coupling constant of 3.6 Hz. Finally, signals for the propyl chain can be observed as two triplets (at 2.84 and 1.02 ppm) and a multiplet at 1.76 ppm (Figure 2). Additionally, the structure of 1 was further confirmed by 13   The strong absorption band can be assigned to π − π* transitions of the terpyridine part, and the shape of the spectrum is similar to previously reported ones for such fivemembered heterocycle-substituted terpyridines [11,19].
The solid was then filtered on a glass sintered funnel and washed with ice-cold 50% ethanol until washings were colorless. The product was dried under vacuum over phosphorus pentoxide. Compound 1 was obtained as a light-yellow solid (4.25 g; 39%). Mp= 98-99 °C. 1 13

Conclusions
A new thiophene-containing terpyridine was prepared and characterized. This ligand features an alkyl chain on the thiophene ring. This resulted in a lowering of the melting point of this type of molecule, a feature that can be interesting in view of future applications (e.g., for the preparation of low melting complexes).
Experiments are currently in progress to incorporate this ligand into organometallic materials. Results will be reported in due course. Funding: This research did not receive specific funding.

Data Availability Statement:
The data from this study are available in this paper and in its supplementary materials.

Conflicts of Interest:
The authors declare no conflict of interest.