The conformational isomerism of 1,3,5,7-tetra-tert-butyl-indacene

In this paper density functional calculations on s-indacene and two alkyl derivatives, 1,3,5,7-tetra-methyl-s-indacene (TMI) and 1,3,5,7- tetra-tert-butyl-s-indacene (TTBI) are reported. It is found that the ‘quasi-delocalized’ ring structure of s-indacene shifts to structures of D2h or C2h symmetry in the derivatives as a function of the alkyl rotation with respect to the indacene ring. Experimental evidence of conformational isomerism is suggested by the TTBI band structure in the region of the first electronic transition.