Thermal extrusion of a one-carbon species from 1,2-benzotropilidene (5H-benzocycloheptene), the benzotropyl (benzocycloheptenyl) free radical, 1,2:5,6-dibenzotropylidene (5H-dibenzo[a,d]cycloheptene), and the 1,2:4,5-dibenzotropyl (dibenzo[a,d]cycloheptenyl) free radical