Fluorescent Sensors involving PET or TICT State Formation
Kerry Mitchell, Xavier Poteau, Alexis Holden, Andrew Brown and Bob Brown,
University of Central Lancashire.
Colette Holmes and David Matthew, BNFL plc
Dongwu Yuan, Shao-Chieh Chang and Ronald E. Utecht, South Dakota State University
David E. Lewis , University of Wisconsin - Eau Claire
Fluorescent materials are now used for a wide variety of sensing
applications and there is considerable current interest in the development of sensors for
metal ions. In developing such systems one seeks both specificity and sensitivity toward
the ion of interest. In addition, compounds which exhibit an increase in fluorescence
intensity (chelation enhanced fluorescence - CHEF) in the presence of the ion and/or a
spectral change (so that a ratiometric sensor not requiring frequent calibration becomes
possible) are attractive.
We are investigating two different approaches to this problem. The first involves the use of compounds which form twisted intramolecular charge transfer (TICT) states. The archetypical example of such compounds is 4-N,N-dimethylaminobenzonitrile (DMABN). On excitation, the locally excited (LE) state of DMABN is produced which emits around 340 nm. Twisting about the bond joining the dimethylamino group to the phenyl ring yields the TICT state which also emits, but at longer wavelength (400 nm+, depending on the solvent).