Stable High-Energy Excited States Observed in a Conjugated Molecule with Hindered Internal Conversion Processes

Abstract

When the excited states of a molecule above its lowest excited state (S n or T n , n > 1) have a sufficient lifetime, photophysical and photochemical processes may occur directly in these high-energy levels, bypassing the Kasha's rule and significantly influencing the system properties. Investigation of the relationship between molecular structure and intramolecular electronic relaxation processes targets molecular design to achieve a long-lifetime higher excited states. Here, we report stable high-energy excited states with lifetimes approaching several nanoseconds in our newly designed and synthesized compound PPI−AnCN. Through experimental and theoretical investigation, we reveal that both large energy gap and poor electronic coupling between the high excited state and the S 1 state are responsible for this stability. More importantly, we find that the emission from the higher exited states can be promoted when the lowest excited state is quenched. This study provides new insights into understanding long-lifetime higher excited states and intramolecular electronic relaxation processes.

Dual Emission: Classes, Mechanisms, and Conditions

“…[71,73] Thel arge DE(S 2 ÀS 1 )v alue should effectively slow down IC in as imple FGR framework;i nf act, am ore thorough treatment with CI reaches the same conclusions. [15,73] Further examples of compounds showing steady-state non-Kasha emission in solution are cyclo [3.3.3]azines [74] as well as triphenylmethane-(TPM-), [75] porphine-, [76] thioketone-, [67] tricarbocyanine (TCC)-, [77] and phenanthroimidazole-type [78] dyes, which show very large f 2 values and also large DE(S 2 ÀS 1 )v alues on the order of 1eV, thus emphasizing the crucial role of alarge energy spacing DE(S 2 ÀS 1 )for the observation of non-Kasha behavior. For new compounds,t his should be crosschecked with quantum-chemical calculations, [79] and by analyzing the PLE spectrum (see Section 2).…”

Heavy‐Atom‐Free Room‐Temperature Phosphorescent Rylene Imide for High‐Performing Organic Photovoltaics

“…Now we have identified the fast generation mechanism of triplet excitons in TPH and PPD, the key objective of this work is to determine the position of triplet states of these two electron acceptors via phosphorescence measurement directly and unambiguously using a spectrometer equipped with a liquid‐nitrogen‐cooled Dewars, which is of significance for OSCs. Here, we used 1,3‐bis(9‐carbazolyl)benzene (mCP) [ 29 ] as the phosphorescent host material with a high E T1 of 2.91 eV and used a mixed solvent (triethylamine [ 30 ] :dichloromethane = 5:1, TEA/DCM) to perform the phosphorescence measurement. Both TPH and PPD present absorption responses from 300 to ≈600 nm in TEA/DCM (Figure S3 , Supporting Information), identical to their spectra in chloroform as reported.…”

Duale Emission: Klassen, Mechanismen und Bedingungen

“…[71,73] Die große S 2 ÀS 1 -Energielücke bedingt bereits im einfachen FGR-Modell eine Verlangsamung der IC;auch die genauere CI-Behandlung kommt zur selben Schlussfolgerung. [15,73] Weitere Beispiele fürS teady-State-non-Kasha-Emission in Lçsung sind Cyclo [3.3.3]azin-, [74] Tr iphenylmethan (TPM)-, [75] Porphin-, [76] Thioketon-, [67] Tr icarbocyanin (TCC)- [77] und Phenanthroimidazol-basierte [78] Farbstoffe,d ie ausreichend große f 2 -Oszillatorstärken und gleichzeitig große DE(S 2 ÀS 1 )-Separation in der Grçßenordnung von 1eVaufweisen;d ies unterstreicht wiederum die zentrale Role einer großen S 2 ÀS 1 -Energielücke fürd as Auftreten des Non-Kasha-Verhaltens. Fürn eue Verbindungen sollte dies mithilfe quantenchemischer Berechnungen [79] sowie durch eine Analyse des PLE-Abbildung 3.…”