Large Inverted Singlet–Triplet Energy Gaps Are Not Always Favorable for Triplet Harvesting: Vibronic Coupling Drives the (Reverse) Intersystem Crossing in Heptazine Derivatives

2021 ◽  
Author(s):  
Fabian Dinkelbach ◽  
Mario Bracker ◽  
Martin Kleinschmidt ◽  
Christel M. Marian
Keyword(s):  
Vibronic Coupling ◽  
Intersystem Crossing ◽  
Triplet Energy ◽  
Energy Gaps ◽  
Triplet Harvesting

scholarly journals Kinetics of thermal-assisted delayed fluorescence in blue organic emitters with large singlet–triplet energy gap

2015 ◽  
Vol 373 (2044) ◽  
pp. 20140447 ◽  
Author(s):  
Fernando B. Dias
Keyword(s):  
Energy Gap ◽  
Delayed Fluorescence ◽  
Threshold Temperature ◽  
Intersystem Crossing ◽  
Triplet Energy ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Kinetics Of ◽  
Triplet Harvesting

The kinetics of thermally activated delayed fluorescence (TADF) is investigated in dilute solutions of organic materials with application in blue light-emitting diodes (OLEDs). A method to accurately determine the energy barrier (Δ E a ) and the rate of reverse intersystem crossing ( k Risc ) in TADF emitters is developed, and applied to investigate the triplet-harvesting mechanism in blue-emitting materials with large singlet–triplet energy gap (Δ E ST ). In these materials, triplet–triplet annihilation (TTA) is the dominant mechanism for triplet harvesting; however, above a threshold temperature TADF is able to compete with TTA and give enhanced delayed fluorescence. Evidence is obtained for the interplay between the TTA and the TADF mechanisms in these materials.

scholarly journals Herzberg-Teller Vibronic Coupling Effect on the Vibrationally-Resolved Electronic Spectra and Intersystem Crossing Rates of a TADF Emitter: 7-PhQAD

2021 ◽  
Author(s):  
Sirong Lin ◽  
Zheng Pei ◽  
Bin Zhang ◽  
Huili Ma ◽  
Wanzhen Liang
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Coupling Effect ◽  
Delayed Fluorescence ◽  
Vibronic Coupling ◽  
Time Dependent ◽  
Rate Coefficients ◽  
Quantitative Prediction ◽  
Intersystem Crossing ◽  
Triplet Energy

Assessing and improving the performance of organic light-emitting diode (OLED) materials require quantitative prediction of rate coefficients for the intersystem crossing (ISC) and reverse ISC (RISC) processes, which are determined not only by the singlet-triplet energy gap and the direct spin-orbit coupling (SOC) at a thermal equilibrium position of the initial electronic state but also by the non-Condon effects such as the Herzberg-Teller vibronic coupling (HTVC) and the spin-vibronic coupling (SVC). Here we applied the time-dependent correlation function approaches to calculate the vibronic absorption and fluorescence spectra and ISC and RISC rates of a newly synthesized multiple-resonance-type (MR-type) thermally activated delayed fluorescence (TADF) emitter, 7-phenylquinolino[3,2,1-de]acridine-5,9-dione (7-PhQAD), with inclusion of the Franck-Condon (FC), HTVC, and Duschinsky rotation effects. It is found that the experimentally-measured ISC rate of 7-PhQAD originates predominantly from the HTVC which increases the ISC rate by more than one order of magnitude while the HTVC effect on the vibronic spectra is negligible. The small discrepancy between the theoretical and experimental rates originates from the neglect of the second-order SVC and the inaccurate excited states calculated by the single-reference time-dependent density functional theory. This work provides a demonstration of what proportion of ISC and RISC rate coefficients of a MR-type TADF emitter can be covered by the contribution of HTVC, and opens design routes that go beyond the FC approximation for the future development of high-performance systems.

Aggregation-induced emission (AIE)-active molecules bearing singlet oxygen generation activities: the tunable singlet–triplet energy gap matters

2019 ◽  
Vol 55 (10) ◽  
pp. 1450-1453 ◽  
Author(s):  
Chengkai Zhang ◽  
Yanqian Zhao ◽  
Dandan Li ◽  
Jiejie Liu ◽  
Heguo Han ◽  
...  
Keyword(s):  
Singlet Oxygen ◽  
Cell Apoptosis ◽  
Near Infrared ◽  
Energy Gap ◽  
Intersystem Crossing ◽  
Triplet Energy ◽  
Oxygen Generation ◽  
Two Photon ◽  
Singlet Oxygen Generation ◽  
Infrared Excitation

Two-photon active photosensitizers showed relatively strong intersystem crossing facilitating 1O2 generation and cell apoptosis with near-infrared excitation.

scholarly journals Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides

2015 ◽  
Vol 17 (36) ◽  
pp. 23468-23480 ◽  
Author(s):  
Sundaram Arulmozhiraja ◽  
Naoki Nakatani ◽  
Akira Nakayama ◽  
Jun-ya Hasegawa
Keyword(s):  
Energy Dissipation ◽  
Rhodobacter Sphaeroides ◽  
Purple Bacteria ◽  
Minimum Energy ◽  
Intersystem Crossing ◽  
Triplet Energy ◽  
Energy Dissipation Mechanism ◽  
Dissipation Mechanism ◽  
Crossing Point

Triplet energy dissipation mechanism of a carotenoid: just bond twisting and stretching lead to minimum energy intersystem crossing point.

Singlet-Triplet Energy Gaps of Quinonoidal Dinitrenes

1996 ◽  
Vol 25 (2) ◽  
pp. 125-126 ◽  
Author(s):  
Shigeaki Nimura ◽  
Osamu Kikuchi ◽  
Tsuguyori Ohana ◽  
Akira Yabe ◽  
Masahiro Kaise
Keyword(s):  
Triplet Energy ◽  
Energy Gaps
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