The　molecular　structures　and　absorption　spectra　of　three　tetrahydroquinoline　dyes　(C2-1,　C1-1,　and　C1-5)　with　a　tetrahydroquinoline　moiety　as　the　electron　donor,　a　cyanoacrylic　acid　moiety　as　the　electron　acceptor,　and　different　thiophene-containing　electron　spacers　were　investigated　by　density　functional　theory　(DFT)　and　time-dependent　DFT　(TD-DFT).　The　calculated　geometries　indicate　that　a　strong　conjugation　is　formed　in　the　dyes　and　the　conjugate　length　increases　with　the　increase　of　spacer　length.　The　interfacial　charge　transfer　between　the　semiconductor　electrode　and　the　tetrahydroquinoline　dyes　are　electron-injection　processes　from　the　excited　dyes　to　the　semiconductor　conduction　band.　The　simulated　absorption　bands　are　assigned　to　pi-pi*　transitions,　which　exhibit　appreciable　red-shift　with　respect　to　the　experimental　bands　owing　to　the　lack　of　direct　solute　solvent　interaction　and　the　inherent　approximations　in　TD-DFT.　Moreover,　the　effect　of　different　spacers　on　the　molecular　structures,　absorption　spectra,　and　photovoltaic　performance　were　comparatively　discussed.