The triplet-state photoisomerizations of a number of ortho-substituted benzonorbornadienes and anti-7,8-benzotricycl0[4.2.2.0~~~]deca-3,7,9-trienes are reported. All of the examples studied underwent di-r-methane rearrangement with preferential benzo-vinyl bridging to the adjacent aryl carbon. For the nitro-and acetylbenzonorbornadienyl cases, the rearrangement was regiospecific. When the substituent group was cyano (96%), methoxy (89.3%), amino (82.6%), methyl (70%), or fluoro (50%), the bonding preference was somewhat less dramatic (degree of ortho bridging given in %). Sensitized irradiation of o-methoxybenzotricyclodecatriene 27 gave rise to a 66:10:24 mixture of 38-OCH3, 39-OCH3, and 40-OCH3. In contrast, cyano derivative 29 afforded an 84:8:8 mixture of 38-CN, 39-CN, and 40-CN. The diminished level of vinyl-vinyl bonding in the latter case ( I 1-12:l vs. 3:l) denotes that concentration of triplet energy in the aromatic moiety promotes benzo-vinyl bridging. The observed regioselectivity is shown to conform to the magnitude of the relevant orbital coefficients as calculated by perturbation theory and supported by PE data.In the preceding paper,' we delineated the striking control exerted by meta substituents on the directionality of benzovinyl bonding from the triplet excited states of benzonorbornadienes and anti-7,8-benzotricycl0[4.2.2.0~~~]deca-3,7,9-trienes. In the case of a n acceptor substituent, fully regiospecific para bridging was observed with ultimate formation of 2. As concerns donor substituents, a marked predilection for