Second generation proton sponges are known with even higher basicity. 1,8-bis(hexamethyltriaminophosphazenyl)naphthalene or HMPN is prepared from 1,8-diaminonaphthalene by reaction with tris(dimethylamino)bromophosphonium bromide in the presence of triethylamine. HMPN has a pK of 29.9 in acetonitrile which is more than 11 orders of magnitude higher than Proton Sponge.
The aromatization of an additional ring in 4,12-Dihydrogen-4,8,12-triazatriangulene is utilized by Al-Yassiri and Puchta to get a representative for a new class of Δ-shaped proton sponges. This compound has a calculated proton affinity of 254 kcal/mol (B3LYP/6-311+G**) and is therefore between 1,8-Bis(dimethylamino)naphthalene and HMPN.