Spin orbit charge transfer intersystem crossing (SOCT-ISC) is a promising approach to develop heavy atom free triplet photosensitizers. However, designing strong visible light harvesting heavy atom free triplet photosensitizer with efficient ISC ability in numerous solvent is still challenging. Most of the SOCT-ISC triplet photosensitizers exhibit efficient ISC only in solvent of particular polarity. To address this challenge, herein two triads (BDP-AN-C-CZ and BDP-AN-N-CZ), composed of carbazole (CZ), anthracene (AN) and bodipy (BDP) moieties were devised. In these triads, distance, relative orientation and position of CZ respect to the AN moiety was varied, to study its effect on the photophysical properties, especially on SOCT-ISC efficiency. Electrochemical studies, steady state and time resolved spectroscopies confirmed a sequential photoinduced electron transfer (PET) process in the triads. The fluorescence of the BDP moiety is quenched and a red shifted CT emission band is observed in the triads, due to enhanced PET effect, compared to the reference BDP-AN dyad. The triad BDP-AN-C-CZ, in which the CZ moiety is directly linked to the AN moiety, shows efficient ISC ability both in low polar and high polar solvents, with unity triplet quantum yield (FT) observed in dichloromethane. Femtosecond transient absorption spectroscopy confirmed the occurrence of a fast charge separation (CS) process (1.8 ps) in BDP-AN-C-CZ as compared to the other triad BDP-AN-N-CZ (4.8 ps) and the reference BDP-AN dyad (7.7 ps). We observed that the SOCT-ISC can be enhanced taking advantage of sequential electron transfer. The triads were implemented in the application of triplet-triplet annihilation (TTA) upconversion showing high upconversion quantum yield (FUC = 18 %). Interestingly, long lived (τ = 118 µs) and solvent dependent color-tunable TTA delayed fluorescence was observed in case of BDP-AN-C-CZ triad.
Published as:
Mahmood, Z., Taddei, M. Rehmat, N., Bussotti, L., Doria, S., Guan, Q., Ji, S, Zhao, J., Di Donato, M.,HuoYong, Y.,Xing,H. Color-Tunable Delayed Fluorescence and Efficient Spin–Orbit Charge Transfer Intersystem Crossing in Compact Carbazole-Anthracene-Bodipy Triads Employing the Sequential Electron Transfer Approach (2020) J. Phys. Chem. C 124(11), 5944-5957 DOI: 10.1021/acs.jpcc.9b11687