Novel cationic intramolecular hydrogen abstraction photosensitizers (IHA-PSs) based on a proposed intramolecular hydrogen abstraction photosensitization (IHAP) mechanism were synthesized and found to have a pronounced photosensitization effect in cycloaliphatic epoxide based cationic UV-curable systems using sulfonium salt photoinitiators. A series of polyol-based photosensitizers were synthesized with naphthalene attached. One photosensitizer, P-Na, was found to have a more pronounced photosensitization effect in three different formulation systems, as revealed by real-time Fourier transform infrared and differential photocalorimetry experiments. Such a phenomenon can be explained by a proposed facile IHAP mechanism, which is possible only with the unique molecular structure of P-Na. The effect of P-Na was further confirmed by comparison with two non-polyol-type photosensitizers. A designed IHA-PS molecule was synthesized with the proposed principles of the IHAP mechanism, and it achieved a photosensitization effect similar to that of P-Na with a much lower molecular weight and fewer hydroxyl groups per molecule. This further validated the proposed MAP mechanism. (c) 2006 Wiley Periodicals, Inc.