Amino derivatives of 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline – Photophysics and implementation of molecular logic switches

Abstract

In the present work, the photopysical properties of the series of 6-amino-substituted 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline (carbazol-, N,N-diphenyl-, N,N-phenyl-1-naphthyl-, N,N-dimethyl-) and with a special attention to the solvatochromism, acidochromism, solid state fluorescence and electron transfer process has been presented. The Lippert-Mataga plot for the compounds under study is clearly non-linear. Additionally, the Kamlet–Taft multilinear regression analysis revealed a significant effect of protic solvents on the energy of the first electronic excited. 6-aryloamino derivatives bind the proton by quinoline moiety, whereas in the case of 6-dimethylamino-pyrazoloquinoline two steps of protonation were observed. Depending on chosen output channel, the pH-dependent fluorescence of N,N-dimethylamino derivative of pyrazoloquinoline can be interpreted as a multilevel logic gate (medium-on-off). In other cases, the analysis of pH-modulated fluorescence led to binary on-off response. An unusual large bathochromic shift of the maximum of fluorescence of N,N-dimethylamino derivative in solid state may be assigned to the formation of charge-transfer complexes.