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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 22, Number 2
BKCSDE 22(2)
February 20, 2001 

Silver Colloidal Effects on Excited-State Structure and Intramolecular Charge Transfer of p-N,N-Dimethylaminobenzoic Acid in Aqueous Cyclodextrin Solutions
Jungkwon Choi, Yanghee Kim, Minjoong Yoon, Seung Joon Lee, Kwan Kim, Sae Chae Jeoung
p-N,N-Dimethylaminobenzoic acid, Intramolecular charge transfer, Cyclodextrin silver colloidal effects.
The silver colloidal effects on the excited-state structure and intramolecular charge transfer (ICT) of p-N,N-dimethylaminobenzoic acid (DMABA) in aqueous cyclodextrin (CD) solutions have been investigated by UV-VIS absorption, steady-state and time-resolved fluorescence, and transient Raman spectroscopy. As the concentration of silver colloids increases, the ratio of the ICT emission to the normal emission (Ia /Ib) of DMABA in the aqueous α-CD solutions are greatly decreased while the Ia /Ib values in the aqueous ß-CD solutions are significantly enhanced. It is also noteworthy that the ICT emission maxima are red-shifted by 15-40 nm upon addition of silver colloids, implying that DMABA encapsulated in α-CD or ß-CD cavity is exposed to more polar environment. The transient resonance Raman spectra of DMABA in silver colloidal solutions demonstrate that DMABA in the excited-state is desorbed from silver colloidal surfaces as demonstrated by the disappearance of νs (CO2-)(1380 cm-1 ) with appearance of ν(C-OH)(1280 cm -1) band, respectively. Thus, in the aqueous ß-CD solutions the carboxylic acid group of DMABA in the excited-state can be readily hydrogen-bonded with the secondary hydroxyl group of ß-CD while in aqueous and α-CD solutions the carboxylic acid group of DMABA has the hydrogen-bonding interaction with water. Consequently, in the aqueous ß-CD solutions the enhancement of the Ia /Ia value arises from the intermolecular hydrogen-bonding interaction between DMABA and the secondary hydroxyl group of ß-CD as well as the lower polarity of the rim of the ß-CD cavity compared to bulk water. This is also supported by the increase of the association constant for DMABA/ ß-CD complex in the presence of silver colloids.
219 - 227
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