Observation of hydrogen-bonding effects on twisted intramolecular charge transfer of p-(N,N-Diethylamino)benzoic acid in aqueous cyclodextrin solutions

Yong Hee Kim, Dae Won Cho, Minjoong Yoon, Dongho Kim

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Abstract

The effects of α- and β-cyclodextrins (CDs) on the twisted intramolecular charge transfer (TICT) emission of p-(N,N-diethylamino)benzoic acid (DEABA) in aqueous solution have been investigated by using steady-state and time-resolved fluorescence techniques. The ratio of the TICT emission to the normal emission increases as β-CD concentration increases, while it decreases significantly upon addition of α-CD. This behavior is in accordance with CD dependent decay times of the TICT and normal emissions, indicating the formation of different 1:1 DEABA/CD inclusion complexes. An increased pKa value of DEABA in the α-CD inclusion complex is determined relative to that of the β-CD complex. The rise time for the TICT emission increases as the β-CD concentration increases, whereas no rise time is observed in the case of the α-CD complex. These results and the size of the diethylamino group clearly suggest that the orientation of the DEABA in the β-CD complex is different from that in the α-CD complex; the carboxyl group of DEABA is encapsulated in the α-CD cavity, whereas it is exposed to the water phase in the β-CD complex. The CD dependences of the TICT fluorescence properties demonstrate that the specific hydrogen bonding between the carboxyl group and water plays an important role in the excited-state TICT.

Original languageEnglish
Pages (from-to)15670-15676
Number of pages7
JournalJournal of Physical Chemistry
Volume100
Issue number39
Publication statusPublished - 1996 Dec 1

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All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Physical and Theoretical Chemistry

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