Long-Lived Photogenerated States of α-Oligothiophene−Acridinium Dyads Have Triplet Character

Abstract

Photoinduced processes, leading to charge-transfer states with extended lifetimes, are of key importance for solar-energy-conversion applications. Utilizing external heavy-atom effect allowed us to photogenerate long-lived transients of electron donor-acceptor dyads. For an electron acceptor and a principal chromophore of the dyads, we selected N-methylacridinium, and for electron donors thiophene, bithiophene, and terthiophene were selected. While the photoinduced charge transfer, mediated by the investigated dyads, occurred in the picosecond time domain, the lifetime of the transients extended to the microsecond time domain. We ascribed the relatively long lifetimes to the triplet character of the observed transients. An increase in the size of the donor lowered the energy of the charge-transfer states of the dyads. When the energy level of the acridinium triplet lies below the energy level of the charge-transfer state, the locally excited triplet accounted for the long-lived transient. For the conjugates with charge-transfer states lying below all other excited states, the long-lived transients were, indeed, the charge-transfer species.

Dipole-Mediated Rectification of Intramolecular Photoinduced Charge Separation and Charge Recombination

“…(b) Spectra from electrochemical measurements recorded at the cathodic and the anodic peak of cyclic voltammograms of Aa and 1-metylpyrene (mPy), respectively (100 mM tetrabutylammonium hexafluorophosphate in MeCN). (c) Absorption spectra of Aa transients recorded using pump−probe spectroscopy (λ ex = 350 nm, 5 μJ per pulse): 47,48 singlet excited state, 1 Aa*, recorded at 10 ps after the pulse for DCM solution; triplet excited state, 3 Aa*, recorded 2 ns after the pulse for solutions containing 1-bromobutane; 40 radical cation, Aa •+ , recorded 2 ns after the pulse for aqueous samples of Aa suspended with a surfactant (10 mM odium dodecyl sulfate) and an electron-acceptor cationic fluorescence quencher, 10 mM CuSO 4 . 49,50 Journal of the American Chemical Society the initial photoinduced charge transfer, we compare the CS rates exhibited by the two donor−acceptor dyads.…”

Building blocks for bioinspired electrets: molecular-level approach to materials for energy and electronics

“…To elucidate the media effects on the electronic properties, we focus on the dependence of the Aa electrochemical potentials on the solvent polarity [64][65][66][67][68] polarity that have electrochemical windows extending over the expected potentials needed for the oxidation of the Aa residues: chloroform (CHCl 3 ), dichloromethane (DCM), benzonitrile (PhCN), acetonitrile (MeCN), and propylene carbonate (PC).…”

Bioinspired molecular electrets: bottom-up approach to energy materials and applications

“…The wavelength, λ 00 , at the crossing point between the intensity-normalized spectra provides an estimate for the zero-to-zero energy, E 00 ¼ hc∕λ 00 , which represents the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) optical gap. 5,65,[69][70][71] Inset: cyclic voltammogram of 5Pip for DCM in the presence of 200 mM tetrabutylammonium hexafluorophosphate (scan rate ¼ 200 mV∕s). (b) Reduction potentials of singly oxidized Aa residues, E ð0Þ (Aa •þ þ e − → Aa), obtained from cyclic voltammetry for solvents with different polarity (as represented by the solvent static relative dielectric constants, ε).…”