Sunlight is a renewable energy source that can be stored in chemical bonds using photochemical reactions. The synthesis of exotic and strained molecules is especially attractive with photochemical techniques because of the associated efficient and mild reaction conditions. We have used complete active space self-consistent field (CASSCF) calculations with an (8,7) active space and the ANO-S-VDZP basis set to understand the photophysics and subsequent photochemistry of a possible cubane precursor tricyclo[4,2,0,0^2,5]octa-3,7-diene (1). The energies were corrected with a second-order perturbative correction CASPT2(8,7)/ANO-S-VDZP. The S₀→S₁ vertical excitation energy of 1 is 6.25 eV, whose nature is π→π^* excitation. The minimum energy path from the S₁ Franck-Condon point leads directly to a 4π-disrotatory electrocyclic ring-opening reaction to afford bicyclo[4,2,0]octa-2,4,7-triene. The 2D potential energy surface scan located a rhomboidal S₁/S₀ minimum energy crossing point that connects 1 and cubane, suggesting that a cycloaddition is theoretically possible. We used the fewest switches surface hopping to study this reaction: 85% of 1,722 trajectories relaxed to 8 products; the major products are bicyclo[4,2,0]octa-2,4,7-triene (30%) and cycloocta-1,3,5,7-tetraene (32%). Only 0.4% of trajectories undergo a [2+2] cycloaddition to form cubane.

阳光是一种可再生能源，可以通过光化学反应以化学键形式存储。由于相关的有效和温和的反应条件，奇异分子和应变分子的合成在光化学技术中特别有吸引力。我们使用具有（8,7）个活动空间和ANO-S-VDZP基础集的完整的活动空间自洽场（CASSCF）计算来了解可能的古巴前体三环[4,2， 0,0 ^2,5 ]八-3,7-二烯（1）。用二阶微扰校正CASPT2（8,7）/ ANO-S-VDZP校正能量。S ₀ →S _1的垂直激发能为1，为6.25 eV，其性质为π→π^*激发。从S ₁ Franck-Condon点开始的最小能量路径直接导致4π-可旋转的电环开环反应，得到双环[4,2,0] octa-2,4,7-三烯。2D势能表面扫描位于连接1和古巴的菱形S ₁ / S ₀最小能量交叉点，这表明环加成理论上是可能的。我们使用最少的开关表面跳变来研究此反应：1,722条轨迹中的85％松弛为8种产品；主要产品是双环[4,2,0] octa-2,4,7-三烯（30％）和环辛-1,3,5,7-四烯（32％）。只有0.4％的轨迹经历了[2 + 2]环加成反应，形成了古巴。