Synthesis and properties of 1,8-Di(2-thienyl)-, 1,8-bis(5,2′-bithiophene-2-yl)-, 1,8-bis(5,2′:5′,2″-terthiophene-2-yl)-, and 1,8-bis(5,2′:5′,2″:5″,2″′-quaterthiophene-2-yl)naphthalenes and related compounds