A Redox-Active π-Extended Tetrathiafulvalene-Based Carbon Nanohoop Featuring Unique Kasha/Anti-Kasha Dual Emissions:...

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 exTTF[10]CPP. 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 exTTF[10]CPP 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 exTTF[10]CPP 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 ^•-/exTTF[10]CPP^•+, which provides sufficient time for charge utilization. This exceptional charge-transfer property enhances the photocurrent in C₆₀⊂exTTF[10]CPP-based cast film, which is 2.43 times higher than that of exTTF[10]CPP alone, highlighting its potential in photoelectronic device.