Spectroscopic study of electronic structure and vibrational properties of all-trans-retinal under solvent polarizability and high-pressure modulation

Abstract

Resonance Raman spectroscopy offers precise insights into the characteristics of the excited and ground-state dynamics, allowing for detailed analysis of electronic structure properties and vibrational information. The resonance Raman spectra of all-trans-retinal (ATR) were studied as a function of high pressure and solvent polarizability using cyclohexane as the solvent. The experimental data showed that high pressure and polarizability affected the electronic structure and vibrational properties of ATR. On this basis, the effects of these two external fields on the stretching vibrational modes of the C–C single and C = C double bonds were investigated. The Raman scattering cross section (RSCS) of the C–C and C = C bonds exhibited blueshifts as the polarizability increased. In the liquid state, the Raman spectra of C–C and C = C bonds exhibit a blueshift, along with a progressive decrease in intensity as pressure increases, and the low-frequency shoulder appeared at approximately 1551 cm⁻¹. In the solid state, the C–C and C = C vibrational modes demonstrate a non-uniform response to high pressure, as evidenced by variations in the slope of the frequency shift versus pressure relationship. In addition, three phases in the pressure range between 0 and 7 GPa were observed. Furthermore, quantum chemical calculations with the density functional theory (DFT) approach used at the B3LYP/6-311G(d,p) theoretical method were successfully employed to explore the structure of the harmonic vibrational modes that cannot be detected by experiments and frontier molecular orbitals (FMOs). This work can help to investigate the impact of external factors on the electronic properties and CC vibrational behavior of linear polyene molecules.