A periodic mesoporous SBA-15 silica containing 4,4-(N'N'-diallylaminophenyl)-2,6-diphenylpyrylium ion (BET surface area of 578 m(2) g(-1), pore size 5.2 nm) exhibits upon excitation at 1064 nm activity for second harmonic generation that is the double than that of an analogous MCM-41 material synthesized under basic conditions using cetyltrimethylammonium bromide. This fact has been explained as arising from the instability of pyrylium to basic pHs. (c) 2005 Elsevier B.V. All rights reserved.