Carbazole–benzimidazole based dyes for acid responsive ratiometric emissive switches.

Three carbazole based benzimidazole derivatives exhibiting the effect of intramolecular charge transfer (ICT) caused by the donor–acceptor interaction between their carbazole and benzimidazole units were synthesized. Their photophysical properties were systematically investigated in various solvents with different polarities. Positive solvatofluorochromic effects were observed with the change of solvent from non-polar to polar for all of the three dyes. The synthesized compounds presented proton-induced absorption as well as ratiometric emission changes, indicating that these compounds might be used as proton sensors. The dyes in their solid state are also able to detect acid vapours. The optimized structures of the dyes and their protonated forms were calculated by density functional theory calculations. [ABSTRACT FROM AUTHOR]