Electrochemiluminescence (ECL) is a powerful transduction technique with a leading role in the biosensing field due to its high sensitivity and low background signal. Although the intrinsic analytical strength of ECL depends critically on the overall efficiency of the mechanisms of its generation, studies aimed at enhancing the ECL signal have mostly focused on the investigation of materials, either luminophores or coreactants, while fundamental mechanistic studies are relatively scarce. Here, we discover an unexpected but highly efficient mechanistic path for ECL generation close to the electrode surface (signal enhancement, 128%) using an innovative combination of ECL imaging techniques and electrochemical mapping of radical generation. Our findings, which are also supported by quantum chemical calculations and spin trapping methods, led to the identification of a family of alternative branched amine coreactants, which raises the analytical strength of ECL well beyond that of present state-of-the-art immunoassays, thus creating potential ECL applications in ultrasensitive bioanalysis.

A peculiar characteristic of open-shell singlet diradical molecules is the presence of a double exciton state (H,H → L,L) among low lying excited states. Recent high-level quantum-chemical investigations including a static and dynamic electron correlation have demonstrated that this state can become the lowest singlet excited state, a diagnostic fingerprint of the diradical system. Here we investigate the performance of less computationally demanding TDDFT calculations by employing two approaches: the spin-flip TDDFT scheme and TD calculations based on unrestricted broken symmetry antiparallel-spin reference configuration (TDUDFT). The calculations are tested on a number of recently synthesized, large conjugated systems displaying from moderate to large diradical character and showing experimental trace of the double exciton state. We show that spin-flip (SF) TDB3LYP calculations in the collinear approximation generally underestimate the excitation energy of the double exciton state. When the molecule displays a strong diradical character, the unrestricted antiparallel-spin reference configuration of TDUDFT calculations is characterized by strongly localized frontier molecular orbitals. We show that under these conditions the double exciton state is captured by TDUB3LYP calculations since it is described by singly excited configurations and its excitation energy can be accurately predicted. Owing to the improved description of the ground state, also the excitation energy of the single exciton H → L state generally improves at the TDUB3LYP level. With regard to the double exciton state, SF TDB3LYP performs slightly better for small to medium diradical character while a large diradical character (and strong orbital localization) is a prerequisite for the success of TDUB3LYP calculations whose quality otherwise deteriorates.

The anisotropy of the n-type charge transport of a fluoro-alkylated naphthalene diimide is investigated in the framework of the non-adiabatic hopping mechanism. Charge transfer rate constants are computed within the Marcus-Levich-Jortner formalism including a single effective mode treated quantum-mechanically and are injected in a kinetic Monte Carlo scheme to propagate the charge carrier in the crystal. Charge mobilities are computed at room temperature with and without the influence of an electric field and are shown to compare very well with previous measurements in single-crystal devices which offer a superior substrate for testing molecular models of charge transport. Thermally induced dynamical effects are investigated by means of an integrated computational approach including molecular dynamics simulations coupled to quantum-chemical evaluation of electronic couplings. It is shown that charge transport occurs mainly in the b,c crystallographic plane with a major component along the c axis which implies an anisotropy factor in very good agreement with the observed value.

On the example of an aggregate of two perylenebisimide (PBI) molecules the character of the lowest excited electronic states in terms of charge transfer (CT) and Frenkel exciton (FE) configurations is investigated as a function of the intermolecular arrangement. A minimal model Hamiltonian based on two FE and two CT configurations at the frontier‐orbitals CIS (FOCIS) level is shown to represent a simple and comprehensible approach providing insight into the physical significance of the model Hamiltonian matrix elements. The recently introduced analysis and diabatization procedure (Liu et al., J. Chem. Phys. 2015, 143, 084106 ) method is used to extract the energies of the configurations and their interactions (the model Hamiltonian parameters) also from the accurate CC2 approach. An analysis in terms of diabatic energy profiles and their interactions shows that the FOCIS parameters give a qualitatively correct description of the adiabatic excited state energy profiles. Comparison with CC2 reveals, however, the presence of avoided crossings at FOCIS level, associated with a large character change (CT/FE) of the excited states as a function of the aggregate structure, which represents the major drawback of FOCIS results. We show that proper amendment of the FOCIS‐derived parameters allows to accurately represent the potential energy surfaces and crossings of the excited dimer states as a function of the aggregate structure. © 2018 Wiley Periodicals, Inc.