Spectroscopic and computational studies of fulvenic molecules

Geometry optimization calculations at the B3LYP/6-311+G(d,p) level have been carried out for fulvene (FU) diphenylfulvene (DPFU), diphenylmethylenefluorene (DPMF), and 9-[pp′-bis(dimethylamino)diphenylmethylene]fluorene (DAMF). The phenyl torsion angles for DPFU, DPMF, and DAMF are predicted to be 46°, 56°, and 49°, respectively. Agreement between experimental NMR data and computed magnetic properties support the prediction that the phenyl twist angle of DAMF is less than that of DPMF. The optimized ground state geometries were used as input for TD-DFT calculations of the electronic spectra of the fulvenic compounds. Agreement between the experimental spectral data and theoretical results is good. The calculations indicate that the S0 → S1 is primarily HOMO → LUMO for FU, DPFU, and DAMF and HOMO − 1 → LUMO for DPMF. Analysis of the nodal properties of the molecular orbitals shows that the HOMO of FU correlates with the HOMO of DPFU, HOMO − 1 of DPMF, and HOMO − 2 of DAMF. The LUMO of the compounds correlate with each other. Thus the lowest energy electronic transition is predicted to be B(B2) ← A(A1) under C2(C2V) symmetry for FU, DPFU and DPMF. Whereas, S0 → S1 is predicted to be A ← A under C2 for DAMF. Assignments for other transitions appearing in the electron spectra are discussed.