303186-16-5Relevant articles and documents
Excited-state double proton transfer in 3-formyl-7-azaindole: role of the nπ* state in proton-transfer dynamics
Chou, Pi-Tai,Wu, Guo-Ray,Wei, Ching-Yen,Shiao, Mei-Ying,Liu, Yun-I
, p. 8863 - 8871 (2000)
3-Formyl-7-azaindole (3FAI) and its derivatives have been synthesized to study the role of the nπ* state in the excited-state double proton transfer (ESDPT) reaction. In 3FAI monomer as well as its associated hydrogenbonded complexes the lowest excited singlet state has been concluded to be in the nπ* configuration. The association constants incorporating the hydrogen bonding formation were determined to be 1.9 × 104 (313 K), 2.2 × 104 (298 K) and 1.8 × 105 M-1 (298 K) for 3FAI dimer, 3FAI/azacyclohexanone and 3FAI/acetic acid, respectively, in cyclohexane. In alcohols, the rate of solvent (e.g., methanol) diffusional migration, forming a 'correct' precursor for ESDPT, is concluded to be much slower than the rate of Sππ(*) → Snπ(*) internal conversion which has been deduced to be 4.37 × 1012 s-1. ESDPT is prohibited in the Snπ(*) state of which the relaxation dynamics are dominated by the rate of Snπ(*) → Tππ(*) intersystem crossing. In contrast, for 3FAI dimer or 3FAI/acetic acid complex possessing intact dual hydrogen bonds the intrinsic ESDPT is competitive with the rate of Sππ(*) → Snπ(*) internal con version, resulting in a prominent imine-like tautomer emission. The results provide the first model among 7AI analogues in which the fast rate of Sππ(*) → Snπ(*) internal conversion serves as an internal clock to examine the mechanism of guest molecules (including the bulk alcohols) assisted ESDPT.
