This study reports systematic optical investigations of monolayers and multilayers of WS₂ and WSe₂. The second harmonic generation (SHG) efficiency exhibits a dramatic even-odd oscillation with the number of layers, consistent with the presence or absence of inversion symmetry in even or odd layers. Photoluminescence (PL) measurements show a transition from an indirect band gap semiconductor in multilayers to a direct-gap one in monolayers. A hot luminescence peak (B) is observed at ~0.4 eV above the prominent band edge peak (A) in all samples. The magnitude of A-B splitting is independent of the number of layers and coincides with the spin-valley coupling strength in monolayers. Ab initio calculations show that this thickness-independent splitting pattern is due to giant spin-valley coupling, which suppresses interlayer hopping at the valence band edge near K points. The study also explores the optical properties of WS₂ and WSe₂ using Raman scattering, SHG, and PL. Raman spectra reveal the presence of specific vibrational modes, with the A₁g mode showing a blue shift with increasing layer number. SHG measurements show a dramatic even-odd oscillation, with negligible SHG in even-layer samples and strong emission in odd-layer samples. PL measurements confirm the transition from indirect to direct band gap and show a significant increase in PL quantum efficiency in monolayers. The A-B splitting is consistent across all layers and is attributed to spin-valley coupling. Ab initio calculations confirm that the A-B splitting is due to giant spin-valley coupling, which suppresses interlayer hopping. This coupling leads to a spin-split valence band edge at K points, with a splitting magnitude of ~0.4 eV. The spin-valley coupling also results in a suppression of interlayer hopping, leading to a uniform splitting pattern across all layers. The study highlights the unique properties of WS₂ and WSe₂, including their spin-valley coupling and potential for spintronics applications. The results demonstrate the importance of symmetry variations and spin-valley coupling in determining the optical and electronic properties of atomically thin tungsten dichalcogenides.This study reports systematic optical investigations of monolayers and multilayers of WS₂ and WSe₂. The second harmonic generation (SHG) efficiency exhibits a dramatic even-odd oscillation with the number of layers, consistent with the presence or absence of inversion symmetry in even or odd layers. Photoluminescence (PL) measurements show a transition from an indirect band gap semiconductor in multilayers to a direct-gap one in monolayers. A hot luminescence peak (B) is observed at ~0.4 eV above the prominent band edge peak (A) in all samples. The magnitude of A-B splitting is independent of the number of layers and coincides with the spin-valley coupling strength in monolayers. Ab initio calculations show that this thickness-independent splitting pattern is due to giant spin-valley coupling, which suppresses interlayer hopping at the valence band edge near K points. The study also explores the optical properties of WS₂ and WSe₂ using Raman scattering, SHG, and PL. Raman spectra reveal the presence of specific vibrational modes, with the A₁g mode showing a blue shift with increasing layer number. SHG measurements show a dramatic even-odd oscillation, with negligible SHG in even-layer samples and strong emission in odd-layer samples. PL measurements confirm the transition from indirect to direct band gap and show a significant increase in PL quantum efficiency in monolayers. The A-B splitting is consistent across all layers and is attributed to spin-valley coupling. Ab initio calculations confirm that the A-B splitting is due to giant spin-valley coupling, which suppresses interlayer hopping. This coupling leads to a spin-split valence band edge at K points, with a splitting magnitude of ~0.4 eV. The spin-valley coupling also results in a suppression of interlayer hopping, leading to a uniform splitting pattern across all layers. The study highlights the unique properties of WS₂ and WSe₂, including their spin-valley coupling and potential for spintronics applications. The results demonstrate the importance of symmetry variations and spin-valley coupling in determining the optical and electronic properties of atomically thin tungsten dichalcogenides.