As　for　the　lasing　of　organic　semiconductor　materials,　novel　semi-conducting　materials　N,N＇-bis(3-methylphenyl)-N,N＇-dipheny1[1,1＇:4＇,1　＇＇-terphenyl]-4,4　＇＇-diamine　(BMT-TPD)　and　N,N＇-bis(3-methylphenyl)-N,N＇-diphenyl-[1,1＇:4＇,1　＇＇:4　＇＇,1＇＇＇-quaterphenyl]-4,4＇＇＇-diamine　(BMQ-TPD)　were　synthesized.　In　contrast　to　the　N,N＇-diphenyl-N,N＇-bis(3-methyl-phenyl)-(1,1＇-biphenyl)-4,4＇-diamine　(TPD),　the　well　known　organic　gain　medium　for　the　lasing,　the　two　new　materials　have　lower　amplified　spontaneous　emission　(ASE)　thresholds　and　enhanced　lasing　performance.　The　molecular　geometries　in　the　electronic　ground　state　and　the　first　optically　excited　state　as　well　as　the　vibrational　modes　of　the　three　compounds　have　been　studied　by　means　of　the　dependent　density　functional　theory　(DFT).　Theoretical　analysis　shows　that,　accompanying　with　the　increased　number　of　central　phenyl　rings,　the　uniform　high-frequency　modes　(around　at　1200,　1300　and　1650　cm(-1))　of　the　three　compounds　are　enhanced,　which　is　driven　by　the　C-H　bending　and　C-C　stretching　in　the　central　phenyl　rings.　Correspondingly,　the　enhanced　vibration　strength　of　the　high-frequency　modes　and　reinforced　vibronic　peak　intensity　bring　out　the　distinct　＂four-level＂　energy　level　scheme　which　benefits　population　inversion　for　lasing　and　leads　to　the　decreased　ASE　threshold.　These　results　indicate　that　the　synthesized　materials　are　good　candidates　to　act　as　active　laser　materials　and　our　work　provides　an　insight　into　the　lasing　of　small　organic　molecules.　(C)　2014　Elsevier　B.V.　All　rights　reserved.