Transients in the 100-ns range, observed by time-resolved laser irradiation of trans- 1 -phenyl-2-(2-naphthyI)ethene (trans-2-NPE) under triplet-sensitized excitation conditions in benzene at 25 OC, are assigned to 2-NPE triplets. The energy of the lowest triplet of 2-NPE is determined to be -49 kcal/mol. Application of high energy sensitizers (e.g., xanthone, benzophenone) yields two transients of 2-NPE with T-T absorption maxima at -400 and -500 nm and lifetimes of 150 and 80 ns, respectively, whereas only one transient is observed by using fluorenone and benzanthrone as sensitizers. The transients are tentatively assigned to two sets of conformationally distinct triplet states. The triplets are efficiently quenched by azulene and oxygen. Analysis of the decay of 2-NPE triplets in the absence and presence of quenchers is based on a recently suggested model involving an equilibrium between trans and twisted triplet states (St e 3p). The equilibrium constants (K) and the rate constants of intersystem crossing (3p4 cult + (1 – a)k) are determined.