Spectroscopic Studies of Hexadecylquinolinium Tricyanoquinodimethanide

Abstract

Hexadecylquinolinium tricyanoquinodimethanide (1), a unimolecular rectifier of electrical current with a large ground-state dipole moment (43 ± 8 D), reveals large hypsochromic shifts of the absorption spectrum. Two fluorescent emissions were observed: one in the visible region (quantum yield φ ≈ 0.01, not solvatochromic) and one in the near-infrared spectrum (weakly solvatochromic). Using a prolate spheroidal cavity model and the absorption maxima measured in eight solvents, the excited-state dipole moment of 1 is estimated as 8.7 D. The NMR spectral lines broaden above 330 K and lose the multiplet structure. The core-level N 1s XPS spectrum reveals the three expected N valence states. The valence-level XPS spectrum can be correlated with theory. Simultaneous cyclic voltammetry and electron spin resonance of the radical anion of 1 shows that the spin density in the LUMO of 1 is concentrated on the tricyanoquinodimethanide portion of the anion. The molecule is clearly zwitterionic in the ground state, bo...