Hybrid porous org.-inorg. mesostructured materials are prepd. which can be used in optical gas sensors in the form of thin films as sensitive layers to detect or det. halogenated gaseous compds., esp. BF3 or BCl3. The org. component can have the general formulas R1(Z1)mC:X1CH[(Z2)nR2]C:X2(Z3)pR3 (I) and R1(Z1)mC:X1C[(Z2)nR2]:CR4(Z3)pR3 (II) with X1 and X2 being O, S, or NH; R4 being OH, SH, or NH2; m, n, p being 0 or 1 with the condition that at least one of them is different from 0; Z1, Z2, Z3 being an aryl or heteroaryl group; and at least one of R1, R2, and R3 represents a (Z4)qR5 group in which q is 0 or 1, Z4 represents a C1-6 satd., nonsatd., linear, or branched hydrocarbon group, or a C3-6 cyclic hydrocarbon group which can optionally contain O, S, or N atoms, and R5 is -Si(Cl)t(OR6)v(R7)w in which v and w are integers from 0 to 3, t is an integer from 0 to 2, under the condition that t + v = 1, 2, or 3, and t + v + w = 3, and R6 and R7 represent a C1-6 satd., nonsatd., linear, or branched hydrocarbon group, or a C3-6 cyclic hydrocarbon group which can optionally contain O, S, or N atoms, or a 5-6 membered aryl or heteroaryl group. R1, R2, and R3 not representing a (Z4)qR5 group can be H, a halogen, -CN, -NO2, a C1-6 linear or branched hydrocarbon group, a C3-6 cyclic hydrocarbon group, or a 5-6 membered aryl or heteroaryl group. Preferably, the compd. is 1-phenyl-3-[4-[2-(triethoxysilyl)ethenyl]phenyl]-1,3-propanedione or 1-[4-(2-triethoxysilylvinyl)-phenyl]-1,3-butanedione. The hybrid porous org.-inorg. mesostructured material is prepd. by sol-gel processing including (a) hydrolysis of a compd. having the general formula M(Cl)x(OR8)r with M being a metal, q and r are integers from 0 up to the valency of the metal M with x + r being equal to the valency of M, and R8 being an org. group, in a mixt. of water, org. solvent, and an acid (b) condensation of the obtained product in the presence of a surfactant, esp. cetyltrimethylammonium bromide, (c) reacting the condensed product with I or II, and (d) thermal treatment of the reaction product obtained in (c) at 120-160° for 24-72 h. The metal M can be Al, Zr, Ti, Nb, Y, V, Ce, or preferably Si.