Synthesis, spectral properties and proton phototransfer reaction in a series of new heterocyclic nitrogen-containing derivatives and analogs of 3-hydroxychromone

of PhD thesis, Kharkov V. N. Karazin National University (March 2009) Charge and proton transfer processes are widely spread in nature. Compounds for which these processes are characteristic are actively investigated for over 50 years. 3Hydroxychromone (3HC) derivatives, which exhibit unique physico-chemical properties as a result of the excited-state intramolecular proton transfer (ESIPT) reaction in their molecules, are subjects of extensive scientific research in this domain. Dual-band emission spectra of these compounds became a basis for development of the novel method of fluorescent analysis – ratiometric detection. The main advantage of this approach is that it doesn’t require the use of external standards and reference samples. This particularity can be decisive and crucial in analysis of biological objects. Years of investigations of various possibilities for the practical application of 3HC derivatives showed them to be capable of probing solvent polarity, viscosity, and proton donor or acceptor ability. These fluorescent dyes can also be used as polypeptide markers, as well as indicators and sensors in the studies of physico-chemical properties of biological objects, for example, intracellular pH, surface electric potential of cell membranes and even for early detection of cell apoptosis. In the past 10 years, the synthesis of 3HC derivatives with additional heterocyclic moieties was extensively developed. Thus, 3HC showing the most long-wavelength fluorescence and the highest quantum yields belong to this series of compounds. 3HC derivatives having heteroaromatic substituents in the position 2 can be considered also as systems with a potential possibility of the alternative Hydrogen bonds formation, and as a result – with a possible alternative excited state proton phototransfer pathway. This particularity opens new and rather intriguing page in the study of the ESIPT process photophysics, and also in the design of new multi-band fluorescent compounds highly effective ratiometric probes with the increased number of data collecting channels. Figure 1. Heterocyclic 3-hydroxychromones under study. 2a-d 1a-e 3a O R