Electrosynthesis and characterization of a novel electrochromic copolymer of N-methylpyrrole with cyclopenta[2,1-b:3,4-b′]dithiophene

Electronic, vibrational, and torsional couplings in N-methylpyrrole: Ground, first excited, and cation states

The electronic spectrum associated with the S₁ ← S₀ (ùA₂←X̃¹A₁) one-photon transition of jet-cooled N-methylpyrrole is investigated using laser-induced fluorescence (LIF) and (1 + 1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy; in addition, the (2 + 2) REMPI spectrum is considered. Assignment of the observed bands is achieved using a combination of dispersed fluorescence (DF), two-dimensional LIF (2D-LIF), zero-electron-kinetic energy (ZEKE) spectroscopy, and quantum chemical calculations. The spectroscopic studies project the levels of the S₁ state onto those of either the S₀ state, in DF and 2D-LIF spectroscopy, or the ground state cation (D₀ ⁺) state, in ZEKE spectroscopy. The assignments of the spectra provide information on the vibrational, vibration-torsion (vibtor), and torsional levels in those states and those of the S₁ levels. The spectra are indicative of vibronic (including torsional) interactions between the S₁ state and other excited electronic states, deduced both in terms of the vibrational activity observed and shifts from expected vibrational wavenumbers in the S₁ state, attributed to the resulting altered shape of the S₁ surface. Many of the ZEKE spectra are consistent with the largely Rydberg nature of the S₁ state near the Franck-Condon region; however, there is also some activity that is less straightforward to explain. Comments are made regarding the photodynamics of the S₁ state.

Visible and near-infrared electrochromic thiophene–diketopyrrolopyrrole polymers

The electrochromic properties are found to depend on the ratio of thiophene to DPP in polymers.