Dual Excited-State Intramolecular Proton Transfer Reaction in 3-Hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one

作者：Chen Chyi Lin; Lin Chun Wei; Hsieh Cheng Chih; Lai Chin Hung; Lee Gene Hsiang; Wang Chih Chieh; Chou Pi Tai^*

来源：Journal of Physical Chemistry A, 2009, 113(1): 205-214.

DOI：10.1021/jp809072a

The synthesis, characterization and fundamental of the dual excited-state proton-transfer properties of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one (1a) are reported. In the electronic ground state, there exist two competitive hydrogen bonding (HB) isomers for 1a. Conformer 1a(O) reveals a five-membered ring HB structure between O-H and carbonyl oxygen, while conformer 1a(N) possesses a six-membered ring HB formation between O-H and pyridyl nitrogen. In a single crystal, the X-ray crystallography unveils an exclusive formation of conformer la(N). In solution such as CH(2)Cl(2), 1a(O) and 1a(N) are in equilibrium, and their respective absorption chromophores are significantly different due to different degrees of hydrogen-bond induced pi electron delocalization. Upon excitation, both conformers 1a(O) and 1a(N) undergo excited-state intramolecular proton transfer (ESIPT) reaction. Following ESIPT, 1a(0) gives rise to a tautomer emission maximized at 534 nm in CH(2)Cl(2). Conversely, due to dominant radiationless quenching processes the tautomer emission for la(N) cannot be obtained with a steady-state manner but can be resolved from time-resolved fluorescence. Time resolved fluorescence estimates an equilibrium constant of 27 /- 5 in favor of 1a(N) in CH(2)Cl(2). Ultrafast ESIPT also takes place for the unique la(N) form in the crystal. Due to the prohibition of quenching processes in the solid state, bright tautomer emission maximized at 540 nm is resolved for 1a(N) (Phi(f) similar to 0.3). The interplay between two HB conformers with on(1a(O))/off(1a(N)) character in tautomer emission may find future applications such as the recognition of organic Lewis acid/base in organic solvents.

• 出版日期2009-1-8
• 单位苏州大学