It is generally believed that monosubstituted polyacetylenes are unlikely candidates for photoluminescence (PL) materials, but we demonstrate here that poly(alkylacetylenes) are a class of highly luminescent monosubstituted polyacetylenes. Poly(alkylacetylenes) -{HC C[(CH 2 ) m R]} n - with R=OCO-Biph-OC 7 H 1 5 [m=2(2), 3(3), 4(4), 9(5)], CO 2 (CH 2 ) 6 OCO-Biph-OC 9 H 1 9 [m=2(6), 8(7)], and OCO-Biph-OCOC 1 1 H 2 3 [m=4(8)] emit strong deep-blue light, readily observable by naked eyes under normal room illumination conditions. The PL intensity of (5) is at least six times higher than that of poly(1-phenyl-1-butyne), a well-known photoluminescent disubstituted polyacetylene.