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 (ΦF=0.37 for 1B[7]‐p and ΦF=0.27 for 2B[7]‐p) than those for the 10‐vertex analogues (ΦF=0.04 for 2A[5]‐p). DFT calculations demonstrate an order of magnitude lower first hyperpolarizability, β(−ω,ω,0), for 2B[7]‐p than that for the 10‐vertex analogue 2A[7]‐p (1.7×10−30 vs. 18.9×10−30 esu at ω=0).