In recent research Lee et al used intramolecular fluorescent exciplex of a magneto-sensitive fluorophore, Phen-(CH2)12-O-(CH2)2-DMA to visualize the magnetic field around nanostructures. [Nano Lett. 11 5367 (2011)] Its fluorescence intensity is increased by up to 80 % at 0.1 T of external magnetic field, which is call magnetic field effect (MFE). The sensitivity to the external magnetic field can be explained by the suppression of the intersystem crossing (ISC) of spin-correlated radical pair generated by photo-induced electron transfer (PET) from DMA to Phen* with UV absorption (355 nm). Such a high MFE is anticipated to long spin-correlation time kept by the chain that holds the proximity between the electron donor and acceptor. However, for better magnetic field images, biological application and simpler optical setup we need to develop new magneto-sensitive fluorophores having higher sensitivity to the magnetic field, higher water solubility and Vis excitation wavelength.
In this poster we present our effort to synthesize Py-COO-(CH2)11-O-(CH2)2-DMA(Figure 1.)as a new magneto-sensitive fluorophore.The previous studies showed that unchained Py/DMA system showed ~10% MFE and a simple methylic carbon chained Py-(CH2)n-DMA showed up to 40% MFE. Substituting the Phen of Phen-(CH2)12-O-(CH2)2-DMA with Py showed ~60% fluorescence enhancement. We introduce -COO- group between Py and carborn chain as a electron withdrawing group to lower the HOMO energy level of Py. We expect a better electron transfer between the electron donor to acceptor and form stronger exciplex that is critical to the magneto-senstivity. Its response to the magnetic field is characterized by a programable bipolar electromagnet.