3-(4-Formylphenyl)-triazole functionalized coumarins as violet-blue luminophores and n-type semiconductors: synthesis, photophysical, electrochemical and thermal properties

Abstract

3-(4-Formylphenyl)-triazole-coumarin hybrid chromophores (FPhTCs) were synthesized in good yields, using a click chemistry protocol, and were also structurally characterized. Their photophysical, electrochemical and thermal properties were measured demonstrating that FPhTCs are luminescent in the blue-violet region of the electromagnetic spectrum, both in solution and the solid state. They showed an electrochemical band-gap values of 2.79 ± 0.08 eV, resistivity values between 10⁴ and 10⁵ Ω cm and are thermally stable up to 225 °C, properties that promise FPhTCs as good candidates for optoelectronic or imaging applications. Their solution and solid state photoluminescent properties are discussed and supported by theoretical calculations.

Scheme 1. Route of synthesis for FPhTC compounds 1a–g. (i) ⁱPrOH-DMF (3 : 1), piperidine, Et₃N, CuCN (10% mol), reflux.

Fig. 1. Normalized absorption and emission spectra of PhTCs 1a–g. (a) Absorption in CH₂Cl₂ solutions 3 × 10⁻⁵ M. (b) Emission in CH₂Cl₂ solutions 10⁻⁶ M. (c) Absorption and (d) emission in thin films formed after three submersions of 15 min in a 2 × 10⁻⁴ M in CH₂Cl₂ solutions.

Fig. 2. Resonance structures showing the electronic delocalization and the D–A behavior of coumarin, FPh and triazole fragments.

Fig. 3. (a) Theoretical absorption spectra obtained by TDDFT BhandHLYP/6-31G (d, p), CPCM solvent model (CH₂Cl₂) (b) Isosurfaces of the HOMO, LUMO, HOMO-1 and LUMO+1 orbitals of 1a, 1c and 1f.

Fig. 4. (a) Voltammograms of 1a–1gvs. SCE. (b) Comparison of resistivity values of 1a–g in solid films.

Fig. 5. Thermograms of compounds 1a–g recorded under air.