Contrasting tunability of quinizarin fluorescence with p-sulfonatocalix[4,6]arene hosts.

This study reveals the intriguing modulations in the photophysics of quinizarin (QZ) on its interaction with p-sulfonatocalix[4]arene (SCX4) and p-sulfonatocalix[6]arene (SCX6) hosts. While the SCX6-QZ system shows the usual reduction in both fluorescence intensity and lifetime, the SCX4-QZ system shows a contrasting effect of enhancement in the fluorescence intensity and reduction in the fluorescence lifetime. Such a contrasting effect is not only unusual but also observed for the first time for any host-guest system. The observed results are justifiably correlated with the changes in both radiative and nonradiative decay rate constants for the SCX4-QZ system.