Influence of the alkyl chain-length on the luminescent properties of 6‑hydroxy-2-naphthoate moieties: Preparation, crystal structure and Hirshfeld surface analysis

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To further explore the luminescent materials, a set of 6‑hydroxyl-naphthoate derivatives have been obtained through the esterification reaction of 6‑hydroxy-2-naphthoic acid with a series of organic alcohols (methanol, ethanol, n-propanol and n-butanol, respectively) in the presence of phenyl sulfonic acid. The title compounds were characterized by FT-IR, elemental analysis (EA), UV–vis spectra, NMR and single-crystal X-ray diffraction. Compounds 1–5 are 6‑hydroxy-2-naphthoic acid, methyl 6‑hydroxy-2-naphthoate, ethyl 6‑hydroxy-2-naphthooate, n-propyl 6‑hydroxy-2-naphthoate and n‑butyl 6‑hydroxy-2-naphthoate, respectively. Compounds 1–5 crystallizes in the space group P21/c, Pna21, P21/n, P21/c and P-1, respectively. The C/OH···O hydrogen bonds can be observed. The luminescent emission maxima of compounds 1–5 can be found at 386, 393, 405, 407 and 420 nm in the solid state, respectively, indicating that the photoluminescent peaks occur the bathochromic-shift with the growth of the alkyl chain-lengths. Additionally, there exists the same order for the quantum yields. Meanwhile, the Hirshfeld surface analysis proves that the H···H interactions can be responsible for the emission maxima of these target compounds. The trend of the melting point decreases with the reduction of O···H interactions, and with the increment of the alkyl chain-lengths. The repulsion energy of the target compounds also shows the same tendency, which can be confirmed by the energy framework analysis.