Intra- and Interlayer Energy Transfer in Planar Systems Based on Amphiphilic Naphthalimide Derivatives

The present work considers the possibility of increasing the information signal of thin-film sensitive element of the sensor based on amphiphilic crown substituted derivative of 4-(acylamino)-1,8-naphthalimide via employment of resonance photoexcitation energy transfer process. In such system, information signal is the fluorescence of acceptor fluorophore (4-alkylamino-1,8-naphthalimide), which is excited upon non-radiative transfer of the energy from excited donor fluorophore (crown containing derivative of 4-(acylamino)-1,8-naphthalimide), crown ether fragment of which is “occupied” by coordination interaction with specific cation and thus does not participate in rapid relaxation of the excitation by the photoinduced electron transfer mechanism. For realization of this goal, the synthesis of novel amphiphilic naphthalimide derivatives is carried out; conditions for obtaining of stable monolayers and Langmuir-Blodgett films based on them are studied. It is established that azadithiacrown substituted amphiphilic fluoroionophore in monolayers at air/mercury and silver perchlorate aqueous solutions interface retains the ability for efficient binding of Ag + and Hg 2+ known for its solutions. Described principle of generation of fluorescent signal using mixed monolayer containing the donor-acceptor couple allows one to increase the value of optical response of the monolayer to the presence of assessed cations by 2.5 times. However, the monolayer fluorescence intensity remains too low for practical application. In order to optimize the conditions of the energy transfer process in more practically important solid-state sensory elements we studied the mechanism of non-radiative photoexcitation energy transfer in the multilayer thin-film system based on amphiphilic naphthalimide derivatives obtained by Langmuir-Blodgett (LB) technique. It is shown that this problem can be solved by regulation of the distance between donor and acceptor layers of LBF. Optimal thickness of the separating layer of stearic acid, which for this system amounted to 7 nm, was determined experimentally. Obtained results open up new perspectives for increase of the information signal reading efficiency, which should find application in development of sensitive elements of sensor devices.