Two bulky alkoxysilane dyes based on nonlinear optical (NLO)-active triphenylamino derivatives possessing high thermal stabilities, without and with a cyano group substitution on the vinylene moiety (TPAH and TPACN, respectively), were synthesized, characterized, and copolymerized with tetraalkoxysilane (TEOS) with the ratio of 1:5. After a poling and curing process, the resulting side-chain-type sol-gel films with excellent optical qualities were achieved. Second-order NLO coefficients, d(33), of 10-20 pm/V have been obtained in the films incorporated with different types of NLO-active dyes. The variation of chromophoric structures on NLO properties was investigated, indicating that the cyano substitution on the vinylene bridge of the chromophore would greatly enhance the temporal stability. This work provides a potential design strategy based on molecular engineering which would lead to more stable dipole orientation.