Charge-transfer transitions between wires and spacers in an inorganic-organic quasi-one-dimensional crystal methylviologen lead iodide

We have studied the optical property and electronic structure of an inorganic-organic quasi-one-dimensional crystal, methylviologen lead iodide. Two absorption bands were observed in the near ultraviolet and visible regions. The one is an absorption band at 3.1 eV with a large oscillator strength, which is assigned to one-dimensional excitons confined in the inorganic chains. The other is a broad band observed between 2.0 and 2.8 eV and attributed to charge-transfer transitions from the lead iodide chains to the methylviologen molecules. From the luminescence excitation spectra, it is found that there are two kinds of charge-transfer transitions from the valence band and the nonbonding state of the inorganic chains to the lowest unoccupied molecular orbital of methylviologen.