Energy Transfer in Near-Orthogonally Arranged Chromophores Separated through a Single Bond

Abstract

A combined experimental and theoretical study shows a significant barrier (ca. 100 kJ/mol) to rotation through the interchromophoric carbon−carbon single covalent (1.49 Å) bond between the naphthalenimide and perylenimide units that prevents coplanarization of the two units in the dyad NP, thereby forcing them to act as independent chromophores/redox centers. Upon photoexcitation, highly efficient energy transfer is observed from the naphthalenimide (energy donor) to the perylenimide (energy acceptor) moiety predominantly through Coulombic coupling, completely isolating the orbital overlap (Dexter-type) interaction between the chromophoric units at such short separation by virtue of their orthogonal arrangement. Because Forster's ideal-dipole approximation ignores the contribution from significant higherorder Coulombic interactions at such short distances between donor and acceptor moieties, the complete coupling was computed from the transition densities, giving an estimate of the energy-transfer rate from the naphthalenimide donor to the perylenimide acceptor of k ET = 2.2 × 10 10 s −1 , in agreement with observations. Ultrafast excitation energy (ca. 40 ps, 90%) and electron (<0.5 ps, 10%) transfer from the singlet excited state of naphthalenimide to the perylenimide moiety competes with further delayed processes in the conjugate NP. Upon excitation at 345 nm, conjugate NP exhibits near-quantitative energy transfer in conjunction with solvent-polarity-dependent (solvatochromic) perylenimide fluorescence, resulting in a remarkable Stoke's shift of ca. 175−240 nm. Favorable photophysical properties such as high fluorescence quantum yield, wide excitation range, ultrafast energy transfer, marginal electron transfer, and large Stoke's shift make this conjugate a potential candidate for biological applications.

Nonparallel Stacks of Donor and Acceptor Chromophores Evade Geminate Charge Recombination

“…A significant energy barrier (ca. 100 kJ/ mol) 22 to rotation between naphthalene and naphthalimide units connected across single covalent bond enforces a non-planar arrangement of the dyad in ACN solution. Spherical/ ring-like architectures of the dyad formed in CHCl3, upon addition of hexane, crystallize as non-parallel stacks (Scheme 1g) of naphthalene and naphthalimide, in contrast to the disordered aggregates proposed for similar architectures.…”

Electronic Modulation of Terrylene Diimides Leading to Core‐Twisting, Tunable Emission and Intermolecular Interactions

“…Synthesis of PMI : This compound was synthesized using a literature procedure . A solution of PDA (9.34 mmol, 3.66 g), 2,6‐diisopropylaniline (5.12 mmol, 0.91 g), zinc acetate dihydrate (7.19 mmol, 1.32 g), and imidazole (275 mmol, 18.70 g) in 8 mL of water was heated at 190 °C for 23 hours in a sealed tube.…”

“…This compound was synthesized using a literature procedure. [37] A solution of PDA (9.34 mmol, 3.66 g), 2,6-diisopropylaniline (…”

Viable access to the triplet excited state in peryleneimide based palladium complex $$^{\S }$$ §

“…Synthesis of PMI and PMI-Br were carried out following our previous reported procedures. 27,44 The synthesized PMI-Br was further reacted with tetrakis(triphenylphosphine) palladium(0…”