Thermal and Photophysical Properties of Highly Quadrupolar Liquid-Crystalline Derivatives of the [closo-B12H12]2- Anion

Two series of 1,12-bis-zwitterionic derivatives of the [closo-B12H12](2-) anion (B), containing either two 4-alkoxypyridinium groups (1B[n]-p) or one 4-alkoxypyridinium and one 4-pentylthianium groups (2B[n]-p), were prepared and their structural (XRD, DFT), thermal, and photophysical properties were compared with those of the analogous derivatives of the [closo-B10H10](2-) anion (1A[n]-p and 2A[n]-p). Some 1,7-derivatives of B were isolated and investigated. Both series 1[n] and 2[n] exhibit nematic and crystalline polymorphism; the 12-vertex derivatives (B) have higher transition temperatures than those of the 10-vertex analogues (A). All compounds fluoresce with quantum yields higher for 1B (Phi(F) = 0.37 for 1B[7]-p and Phi(F) = 0.27 for 2B[7]-p) than those for the 10-vertex analogues (Phi(F) = 0.04 for 2A[5]-p). DFT calculations demonstrate an order of magnitude lower first hyperpolarizability, beta((-omega,omega,0)), for 2B[7]-p than that for the 10-vertex analogue 2A[7]-p (1.7 x 10(-30) vs. 18.9 x 10(-30) esu at omega = 0).