• Dimeric conformation sensitive electronic excited states of tetracene congeners and their unconventional non-fluorescent behaviour

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    • Keywords

       

      Non-fluorescent J-aggregates; transition dipole moment; DFT; excited state; singlet fission

    • Abstract

       

      Unconventional non-fluorescent J-aggregates of Tetracene (TC) and Naphtho[2,1,8-qra]tetracene (NT) were witnessed and their consequent dramatic quenching was unravelled by a steady state, time-resolved and transient spectroscopy in conjunctionwith excited state density functional calculations. The TC O-aggregate with slippage angle θ = 22.3◦ ˂ 54.7◦ exhibited substantial transition dipole moment (TDM) for both lower (2.79 D) and higher (1.59 D) energy singlet excitations, while, NT formed an ideal J-aggregate (polarizationangle, α ~ 0◦ ) with a predominant TDM to only a lower excitonic state (2.69 D). Subsequently, their unusual quenching was quantified with large drops in the photoluminescence quantum yields (PLQY) from 0.116 to 0.002 upon TC O-aggregation and from 0.478 to 0.038 upon NT J-aggregation. These intense PL drops were systematically investigated for possible occurrence of excimer-like emission quenching and/or photodegradation of the TC core unit. In view of the TC O-aggregates exhibiting a perfect energetic balance between the singlet (2.34 eV) and triplet (1.28 eV) energies for singlet fission (SF) and a concomitant delayed fluorescence signal, their S1 decay characteristics were attributed to SF followed by an inverse triplet-triplet recombination.In contrast, the energetic imbalance (E(S1) ˂ 2xE(T1)) in NT J-aggregates permitted only forward processof SF and the resulting long-lived triplet formation was traced with a positive transient absorption (T1 → Tn) band at 500 nm. Accordingly, the singlet excited state (S1) dynamics of TC O- and NT J-aggregates, being largely dominated by SF, depicted a depleted S1 population, accounting for the large deviation from aggregation induced enhanced emission, exhibited by classical dye J-aggregates.

    • Author Affiliations

       

      N AGGARWAL1 2 A PATNAIK1

      1. Colloids and Interface Chemistry Laboratory, Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India
      2. Department of Chemistry and Biochemistry, Sharda University, Greater Noida, Uttar Pradesh 201 310, India
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