Direct Evidence of Significantly Different Chemical Behavior and Excited-State Dynamics of 1,7- and 1,6-Regioisomers of Pyrrolidinyl-Substituted Perylene Diimide

Side-chain substitutions have important influence on the aggregation of perylene diimide (PDI), which show a great impact on their excited-state dynamics as well. Herein, by employing photoluminescence (PL), time-resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopy, we investigated excited-state dynamics of two perylene diimide (PDI) derivative amorphous films, i.e. undecane-substituted PDI (PDI-1) and diisopropylphenyl-substituted PDI (PDI-2), fabricated with spin coating method. Femtosecond transient absorption spectra reveal that both films show pronounced ground state bleach (GSB) with lifetime longer than 10 ns while the relaxation of excited state absorption (ESA) has typical lifetime less than 1 ns. The significant feature of excited state decay in PDI-2 is dominated by transforming the singlet excited state into two triplet states via singlet fission, which is evidenced by the appearance of triplet state absorption. By contrast, the absence of triplet state absorption and the appearance of long-lived emission species in PDI-1 suggest that the decay of excited-like state could be dominated by the formation of excimer. Our present study reveals for the first time that the singlet fission does occur in amorphous PDI film, the study also demonstrates that side-chain substitutions have great impact on the excited-state dynamics of PDI.

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ULTRAFAST XUV SPECTROSCOPY TO PROBE CONICAL INTERSECTIONS AND EXCITED STATE DYNAMICS

Proceedings of the 74th International Symposium on Molecular Spectroscopy ◽

10.15278/isms.2019.wk01 ◽

2019 ◽

Author(s):

Arvinder Sandhu

Keyword(s):

Excited State ◽

Conical Intersections ◽

Excited State Dynamics ◽

Xuv Spectroscopy

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Excited-State Dynamics in the RNA Nucleotide Uridine 5’-Monophosphate Investigated by Femtosecond Broadband Transient Absorption Spectroscopy

10.26434/chemrxiv.7860023 ◽

2019 ◽

Author(s):

Matthew M. Brister ◽

Carlos Crespo-Hernández

Keyword(s):

Excited State ◽

Excited States ◽

Ground State ◽

Transient Absorption ◽

Electronic Energy ◽

Transient Absorption Spectroscopy ◽

Electronic Relaxation ◽

Vibrationally Excited ◽

Excited State Dynamics ◽

Π State

Damage to RNA from ultraviolet radiation induce chemical modifications to the nucleobases. Unraveling the excited states involved in these reactions is essential, but investigations aimed at understanding the electronic-energy relaxation pathways of the RNA nucleotide uridine 5’-monophosphate (UMP) have not received enough attention. In this Letter, the excited-state dynamics of UMP is investigated in aqueous solution. Excitation at 267 nm results in a trifurcation event that leads to the simultaneous population of the vibrationally-excited ground state, a longlived 1nOπ* state, and a receiver triplet state within 200 fs. The receiver state internally convert to the long-lived 3ππ* state in an ultrafast time scale. The results elucidate the electronic relaxation pathways and clarify earlier transient absorption experiments performed for uracil derivatives in solution. This mechanistic information is important because long-lived nπ* and ππ* excited states of both singlet and triplet multiplicities are thought to lead to the formation of harmful photoproducts.

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