Organic fluorescent molecules undergoing intramolecular proton transfer in excited state (ESIPT) have been important components in the search for highly efficient organic (opto-)-electronic devices. Their unique photophysical properties are translated into the characteristics of the bulk materials and are easily tailored by alteration of the substituents on the periphery of the p-frameworks. With multiple applications spanning laser dyes, bioimaging and UV-photostabilizers, they attracted attention from many vantage points. The new class of ESIPT-capable molecules, benzo[a]imidazo[5,1,2-cd]indolizines bearing 2-hydroxyphenyl substituent were prepared in straightforward manner from imidazo[1,2-a]pyridines via tandem [8+2]cycloaddition-[2+6+2]dehydrogenation reaction. The relationship between the structure and photophysical properties was thoroughly elucidated by comparison with simple analogues i.e. 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridines. While compared with parent 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridines the new chromophores strongly absorb blue light and emit in the yellow part of the spectrum. In contrast to 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridines, emission of p-expanded dyes in protic solvents is usually weaker than in aprotic ones, where they exhibit large Stokes shifts (5500-7000 cm-1). Unlike in solution, in the solid state luminescence for benzo[a]imidazo[5,1,2-cd]indolizines is shifted at average, by 100 nm relative to the fluorescence of the corresponding imidazo[1,2-a]pyridines, which results in relatively strong (Ffl = 0.18-0.27) emission of the red light.

Novel, emission-tunable, and ESIPT-capable organic fluorophores

248th National Meeting (2014)

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