Open AccessPhenothiazine–Quinoline Conjugates Realizing Intrinsic Thermally Activated Delayed Fluorescence and Room‐Temperature Phosphorescence: Understanding the Mechanism and Electroluminescence Devices
Author(s) -
Acharya Nirmalya,
Hasan Monirul,
Dey Suvendu,
Lo Shih-Chun,
Namdas Ebinazar B.,
Ray Debdas
Publication year - 2021
Publication title -
advanced photonics research
Language(s) - English
Resource type - Journals
ISSN - 2699-9293
DOI - 10.1002/adpr.202000201
Subject(s) - phosphorescence , intersystem crossing , homo/lumo , electroluminescence , photochemistry , quinoline , singlet state , fluorescence , materials science , phosphorescent organic light emitting diode , excited state , quantum efficiency , acceptor , chemistry , optoelectronics , molecule , atomic physics , physics , optics , nanotechnology , layer (electronics) , organic chemistry , condensed matter physics
Understanding the local triplet ( 3 LE), charge transfer triplet ( 3 CT), and charge transfer singlet ( 1 CT) is of great importance in designing thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) materials for their use in organic light‐emitting devices (OLEDs), sensing, and bioimaging. Herein, two phenothiazine–quinoline conjugates (PTzQ1, PTzQ2) in which the donor (PTz) and acceptor (Q1, Q2) parts are held in near‐orthogonal orientation that gives rise to spatial separation of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are reported. Photophysical studies of both conjugates along with their individual components (PTz, Q1, Q2) show that TADF occurs via reverse intersystem crossing (rISC) from the upper‐level local triplet ( 3 LE) to lower‐level singlet 1 CT mediated by vibronic coupling between 3 LE and 3 CT, whereas RTP is realized from 3 LE. It is found that all three excited states are close in energy, 0.16–0.19 eV ( 3 LE− 1 CT), 0.02–0.03 eV ( 1 CT− 3 CT), and 0.14–0.16 eV ( 3 LE− 3 CT) with the order of 3 LE > 1 CT > 3 CT. Both conjugates exhibit a high rate constant of rISC ( k rISC , 7.9–9.7 × 10 5 s −1 ), resulting in external quantum efficiency (EQE) values of ≈4.7% (solution processed) with emission from both RTP and TADF components.