Tetracene was found to photodimerize at a lower rate than anthracene. 2d By irradiation of a suspension in benzene (1 × 10 - 3 M), it was reported to form two photodimers: head-to-head (hh), or planosymmetric, and head-to-tail (ht), or centrosymmetric. 2c To our knowledge, no photodimer