Vapor-phase metal–organic photoresists are promising for nanoscale lithography because they combine solvent-minimized processing, conformal ultrathin-film formation, and inorganic-network-enabled pattern stability. However, the molecular origin of their radiation-induced solubility switching remains insufficiently resolved. Here, we report a molecular-layer-deposited titanium–dienediol hybrid photoresist, Ti–DVG, prepared from a titanium precursor and 1,5-hexadiene-3,4-diol. The hydroxyl groups enable sequential molecular layer deposition, while the terminal alkenes introduce unsaturated carbon environments that undergo irradiation-induced transformation within the Ti–organic network. Ti–DVG exhibits nearly linear growth at ca. 0.10 nm cycle^-1, smooth continuous morphology, and a negative-tone response after electron-beam exposure and development. Electron-beam lithography produces continuous 25 nm line/space patterns with line-edge roughness values of 2.347–2.959 nm, while low-contrast limiting features down to approximately 5.2 nm are observed under size-specific exposure conditions, including the use of thinner films for the sub-10 nm tests. EUV interference lithography further resolves dense patterns with half-pitches down to 15–18 nm. Complementary FTIR, background-subtracted outgassing, XPS, repeated-scan XPS, and Raman analyses collectively support ligand transformation, volatile-species evolution, oxygen-environment redistribution, and formation of Ti–O-rich local structures. This work establishes a mechanistically traceable design strategy for vapor-phase hybrid photoresists.