Impact of Charge-Resonance Excitations on CT-Mediated J-Type Aggregation in Singlet and Triplet Exciton States of Perylene Di-Imide Aggregates: A TDDFT Investigation

Abstract

The modulation of intermolecular interactions upon aggregation induces changes in excited state properties of organic molecules that can be detrimental for some optoelectronic applications but can be exploited for others. The time-dependent density functional theory (TDDFT) is a cost-effective approach to determining the exciton states of molecular aggregates, and it has been shown to provide reliable results when coupled with the appropriate choice of the functional. Here we apply a general procedure to analyze the aggregates’ exciton states derived from TDDFT calculations in terms of diabatic states chosen to coincide with local (LE) and charge-transfer (CT) excitations within a restricted orbital space. We apply the approach to study energy profiles, interstate couplings, and the charge-transfer character of singlet and triplet exciton states of perylene di-imide aggregates (PDI). We focus on the intermolecular displacement along the longitudinal translation coordinate, which mimics different amounts of slip-stacking observed in PDI crystals. The analysis, in terms of symmetry-adapted Frenkel excitations (FE) and charge-resonance (CR) states and their interactions, discloses how the interchange of the H/J character for small longitudinal shifts, previously reported for singlet exciton states, also occurs for triplet excitons.

Eclipsed and Twisted Excimers of Pyrene and 2-Azapyrene: How Nitrogen Substitution Impacts Excimer Emission

“…To this end, a diabatization procedure can be used to determine the linear combination of the and (diabatic) states corresponding to each computed (adiabatic) exciton state [ 39 , 40 , 46 , 47 , 48 , 49 , 50 , 66 ]. Here, we adopt a diabatization approach that we have developed and applied to unravel the nature of the exciton states of several PAH dimers computed at the TD-DFT level [ 55 , 66 , 67 , 68 ]. The details were described in these previous works and can be found in Section 3 and in the Supporting Information section.…”

“…However, we believe that any eventual unbalanced description is expected to be similar for both molecules/dimers given the similar structural and electronic nature of the excited/excimer states. Furthermore, we note that this functional has been successfully used in the discussion of exciton states of several PAH aggregates [ 55 , 67 , 68 , 74 ].…”

“…The excitation energies were obtained using TD-DFT calculations and using the Tamm–Dancoff approximation (TDA) [ 75 ]. We adopted the ωB97X-D functional [ 76 ] since it was shown to provide a suitable description of the character in the singlet excitons of other PAH dimers [ 45 , 55 , 67 , 68 ] and the def2-SVP basis set. All quantum chemical calculations were carried out using Gaussian16 [ 77 ].…”

Energy landscape of perylenediimide chromophoric aggregates

“…Understanding the strength of non-covalent interactions is quintessential in realising the structure-property relationships in aggregates. 7,8 Based on the relative orientation of transition dipole moments corresponding to S 0 -S 1 transition in two monomer units, quantified by the slip angle (y), molecular exciton theory 9,10 categorises aggregates into different classes (Fig. 1).…”

Dedication: Commemorative Issue in Honor of Professor Karlheinz Schwarz on the Occasion of His 80th Birthday

“…We can notice the large panel of scientific topics covered by Karlheinz's knowledge. We deeply acknowledge the following contributions related to spectroscopy by Manuel Yañez et al [12], Juan-Carlos Sancho-García and Emilio San-Fabián [13]; excited states by Ágnes Nagy [14], Kalidas Sen et al [15] and Fabrizia Negri et al [16]; DFT developments by Fabio Della Sala et al [17], Mathias Rapacioli and Nathalie Tarrat [18], Emmanuel Fromager et al [19], José Manuel García de la Vega et al [20] and Harry Ramanantoanina [21]; results analysis by Andreas Savin et al [22] and Manuel Richter et al [23]; and, of course, the solid state and surfaces by Leila Kalantari and Fabien Tran et al [24], Denis Salahub et al [25], Peter Blaha et al [26], Samuel B. Trickey [27], William Lafargue-Dit-Hauret and Xavier Rocquefelte [28], Tzonka Mineva and Hazar Guesmi et al [29]. (H.C.)…”