Electronic structure of tetraphenyldithiapyranylidene (DIPS ϕ4) N. El-Khatib, M. Maitrot, H. Chermette, L. Porte and H. Strzelecka J. Chim. Phys., 84 (1987) 839-842 Published online: 13 June 2017 DOI: 10.1051/jcp/1987840839