▎ 摘　　要

The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S-0), becomes exergonic in the first triplet state (T-1). This is in line with Baird's rule, which tells that benzene is antiaromatic and destabilized in its T-1 state and also in its first singlet excited state (S-1), opposite to S-0, where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic aromatic hydrocarbons (PAHs) to various extents undergo metal-free photochemical (hydro) silylations and transfer-hydrogenations at mild conditions, with the highest yield for naphthalene (photosilylation: 21%). Quantum chemical computations reveal that T-1-state benzene is excellent at H-atom abstraction, while cyclooctatetraene, aromatic in the T-1 and S-1 states according to Baird's rule, is unreactive. Remarkably, also CVD-graphene on SiO2 is efficiently transfer-photohydrogenated using formic acid/water mixtures together with white light or solar irradiation under metal-free conditions.