Jump to main content
Jump to site search

Issue 9, 1996
Previous Article Next Article

Temperature effects on dual emission from ion pairs produced by excited-state proton transfer in the 1-naphthol–triethylamine system

Abstract

1-Naphthol (ROH)–triethylamine(NEt3) hydrogen-bonded systems in non-polar rigid matrices at 77 K show dual fluorescence ascribable to the contact ion pair (CIP), with an in-plane orientation between excited naphtholate and alkylammonium ions, and the separated ion pair (SIP) with an out-of-plane orientation between them. However, at room temperature it was found that there was remarkable quenching of the excited singlet state of the ROH–NEt3 hydrogen-bonded system. Using nanosecond time-resolved emission spectroscopy, temperature effects on the fluorescence-decay kinetics of the ROH–NEt3 system has been studied in polyethylene film and methylcyclohexane–isopentane (MP, 3:1 vol.: vol.) to obtain the excited state behaviour of CIP and SIP. The fluorescence intensities and peaks did not change in the temperature range 77–100 K. Above 100 K, a gradual red shift of the total fluorescence peak with loss of intensity was observed, the effect being more pronounced in MP, especially after the glass-softening temperature (ca. 115 K). Two different quenching processes were found to be operative. Rapid quenching competing with excited-state proton transfer in both hydrogen-bonded systems occurred at high temperatures (> 100 K). This resulted in a considerable decrease of the total fluorescence quantum yield (ϕΣ) with no significant change in fluorescence lifetimes in the temperature range 100–130 K. The quenching mechanism might be a fast internal conversion due to the out-of-plane bending motion of O–H ⋯ N bond. Above 130 K, a new quenching process resulting in the decrease of fluorescence lifetimes of both SIP and CIP also appeared. This dynamic quenching of excited ion pairs is probably caused by a charge–transfer interaction. In addition, from the appearance of neutral ROH phosphorescence, enhanced intersystem crossing and subsequent reverse proton transfer in the triplet state might be taking place.

Back to tab navigation

Article information


J. Chem. Soc., Faraday Trans., 1996,92, 1481-1486
Article type
Paper

Temperature effects on dual emission from ion pairs produced by excited-state proton transfer in the 1-naphthol–triethylamine system

A. K. Mishra and H. Shizuka, J. Chem. Soc., Faraday Trans., 1996, 92, 1481
DOI: 10.1039/FT9969201481

Search articles by author

Spotlight

Advertisements