Developing functionalized cycloparaphenylenes (CPPs) that respond to various stimuli, particularly redox, remains challenging yet crucial for advanced nanocarbon applications. Here, we report the exploration of the synergy between the concave π-extended tetrathiafulvalene (exTTF) and the curved CPP scaffold for constructing the rigid, conjugated nanohoop exTTF10CPP. X-ray analysis reveals a unique spherical packing arrangement in which six adjacent nanohoops interlock through concave and convex interactions. Interestingly, fluorescence studies revealed that exTTF10CPP exhibited unexpected anti-Kasha emissions originating from higher excited states, along with Kasha emission from S1 excited state in toluene and THF. However, in a PMMA film, it displayed a redshifted Kasha emission. The unique Kasha/anti-Kasha dual-emission behavior represents a rarely explored photophysical phenomenon within exTTF derivatives and nanocarbon-based systems. Ultraviolet-Visible (UV-vis) absorption investigations showed that exTTF10CPP demonstrated reversible redox responsiveness with tunable binding affinity for C60 up to 1.92 × 106 M-1. Notably, femtosecond transient absorption measurements further revealed a prolonged lifetime of the charge-separated state, C60 •-/exTTF10CPP•+, which provides sufficient time for charge utilization. This exceptional charge-transfer property enhances the photocurrent in C60⊂exTTF10CPP-based cast film, which is 2.43 times higher than that of exTTF10CPP alone, highlighting its potential in photoelectronic device.
Wu et al. (Mon,) studied this question.