The Influence of Internal Charge Transfer on Nonradiative Decay in Substituted Terthiophenes

Abstract

Photophysical data for a series of end substitued 3',4'-dibutyl-2,2':5',2''-terthiophenes are reported. Static absorption and fluorescence, quantum yields, time-resolved fluorescence, and time- and frequency-resolved pump-probe spectra are applied to investigate excited state relaxation in bromo, nitro, and tricyanovinyl substituted species in a variety of solvents. The effect of solvent polarizability and end-group substitution is discussed in the context of charge transfer in the excited state and its impact on nonradiative decay rates. In solution at room temperature, both symmetric and asymmetric addition of electron withdrawing end groups generate an excited state with substantial charge transfer character. Solvent polarizability has a significant influence on the excited state dynamics in the charge transfer compounds. Examples include a 20-fold reduction in the intersystem crossing rate going from hexane to toluene and an order of magnitude increase in the internal conversion rate between toluene and acetone. The results demonstrate that the impact of the substituents on intramolecular charge transfer, and the resulting amplification of the interactions between the excited state(s) and the local molecular environment, can dramatically change the excited state relaxation dynamics in substituted terthiophenes.

Development of Pyrene Derivatives as Promising n‐Type Semiconductors: Synthesis, Structural and Spectral Properties

“…As shown in Figure , the cyano‐containing compound 3 presented the absorption maximum at 358 nm, and the dicyanovinylene‐containing compounds 1 , 2 and 4 presented the large bathochromic shift. It was explainable by two reasons: the strong electron‐withdrawing ability of dicyanovinylene group and large molecular coplanarity, in agreement with the behavior of the substituted terthiophenes, and a large steric hindrance in 3 molecular structure, which reduced the electron coupling between the pyrene core and thiophene moiety . 1,8‐substituted 1 and 1,6‐substituted 2 are isomers, and they had the similar absorption profiles, indicating that the absorption spectra were not significantly affected by the 1,6‐ or 1,8‐substitution pattern, in good agreement with the report about the pyrene derivaitves 1,6‐ and 1,8‐substituted with 2‐[1,8]naphthylridinyl and thienylphenothiazine .…”

Effect of extending conjugation via thiophene-based oligomers on the excited state electron transfer rates to ZnO nanocrystals

“…The experimental setup has been reported previously. 20 Samples in a 1 cm quartz cell were excited using a 40 MHz diode laser (Picoquant LDH-P-C-375) at 375 nm and 40 MHz diode laser (Picoquant LDH-P-C-470) at 470 nm. Sample emission was detected using an avalanche photodiode at a right-angle geometry at the exit of a double monochromator (Jobin-Yvon TRIAX-320).…”

Preparation, Characterization, Redox, and Photoinduced Electron‐Transfer Properties of the NIR‐Absorbing N‐Ferrocenyl‐2‐pyridone BODIPYs

“…[21] Transient Absorption Spectroscopy: The pump-probe setup has been described previously. [22] A homebuilt, amplified Titanium:Sapphire-based laser system produced 0.5 mJ, 800 nm pulses at 1 kHz centered at 800 nm. The output was divided to produce the excitation and probe pulses.…”