PHOTOISOMERIZATIONS OF THE PHOTOCHROMIC ANIL SALICYLIDENE-1-NAPHTHYLAMINE IN 3-METHYLPENTANE

The results of a nanosecond flash-photolysis study with solutions of s alicylidene-1-naphthyl-amine (SN) in 3-methylpentane (3MP) at ambient and at low temperatures are reported. Besides a newly discovered tripl et state, two photochromic transients (PCTs) are formed after excited state intramolecular proton-transfer (ESIPT) has taken place. Above 14 0 K the formation of a quinoid trans-keto tautomer (K-1(tr)) prevails. At 100 K a second PCT is observed in steady-state experiments which w e tentatively assign to a twisted conformer of the keto form of SN. Th e transient K-1(tr) re-enolizes in dry 3MP by second-order double prot on-transfer; in the presence of 10(-4) M methanol the re-enolization o f K-1(tr) is proton catalyzed and the lifetime of K-1(tr) is shortened by more than two orders of magnitude. The properties of the flexible SN are compared with two other rotationally hindered 'ESIPT molecules' .