Rational design of near‐infrared absorbing organic dyes: Controlling the HOMO–LUMO gap using quantitative molecular orbital theory

Hamlin

Lammertsma

et al. 2019

Chemistry A European J

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The unusually fast Diels–Alder reactions of [5]cyclophanes were analyzed by DFT at the BLYP‐D3(BJ)/TZ2P level of theory. The computations were guided by an integrated activation‐strain and Kohn–Sham molecular orbital analysis. It is revealed why both [5]metacyclophane and [5]paracyclophane exhibit a significant rate enhancement compared to their planar benzene analogue. The activation strain analyses revealed that the enhanced reactivity originates from 1) predistortion of the aromatic core resulting in a reduced activation strain of the aromatic diene, and/or 2) enhanced interaction with the dienophile through a distortion‐controlled lowering of the HOMO–LUMO gap within the diene. Both of these physical mechanisms and thus the rate of Diels–Alder cycloaddition can be tuned through different modes of geometrical distortion (meta versus para bridging) and by heteroatom substitution in the aromatic ring. Judicious choice of the bridge and heteroatom in the aromatic core enables effective tuning of the aromatic Diels–Alder reactivity to achieve activation barriers as low as 2 kcal mol−1, which is an impressive 35 kcal mol−1 lower than that of benzene.

Section: Resultsmentioning

confidence: 49%

“…Heteroatom-substituted benzene derivatives of main group elements show interesting electronic properties, such as asmaller H-L gap, [32] as wellasa nenhanced cycloaddition reactivity. The latter can also be addressed through means other than distortion, such as heteroatom substitution in the aromatic core.…”

Section: Resultsmentioning

confidence: 99%

Dual Activation of Aromatic Diels–Alder Reactions

Hamlin

Lammertsma

et al. 2019

Chemistry A European J

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“…Ah eteroatomi na(poly)cyclic aromatic compound can serve as an auxiliary electron donor and/ora cceptor and changes energy levels, shapes of the frontier orbitals, and the geometry of the aromatic core. [8,9,50] Upon replacing one of the unsubstituteda romatic carbon atoms of 11 for either as ilicon (12)o raphosphorus (13)a tom, DE H-L decreases due to both destabilization of the p-HOMO ands tabilization of the p*-LUMO. [8,9,50] Upon replacing one of the unsubstituteda romatic carbon atoms of 11 for either as ilicon (12)o raphosphorus (13)a tom, DE H-L decreases due to both destabilization of the p-HOMO ands tabilization of the p*-LUMO.…”

Section: Complexmodel Systemsmentioning

confidence: 99%

“…[8,9,50] Upon replacing one of the unsubstituteda romatic carbon atoms of 11 for either as ilicon (12)o raphosphorus (13)a tom, DE H-L decreases due to both destabilization of the p-HOMO ands tabilization of the p*-LUMO. [8] Moreover,S i presentsahigh-lying occupied p p orbital, whereas Pp resents a low-lyinge mpty p p orbital, which mixes with the p framework of the conjugated diene (highlighted in red, see Figure 6a), both of whichr esult in ad ecreased DE H-L .A dditionally,t he outof-plane distortion caused by the enhanced steric repulsion betweent he larger heteroatom and its neighboringc arbon atoms( Da(11-13) = 48)a dds to ad ecrease in DE H-L . [8] Moreover,S i presentsahigh-lying occupied p p orbital, whereas Pp resents a low-lyinge mpty p p orbital, which mixes with the p framework of the conjugated diene (highlighted in red, see Figure 6a), both of whichr esult in ad ecreased DE H-L .A dditionally,t he outof-plane distortion caused by the enhanced steric repulsion betweent he larger heteroatom and its neighboringc arbon atoms( Da(11-13) = 48)a dds to ad ecrease in DE H-L .…”

Section: Complexmodel Systemsmentioning

confidence: 99%

“…[4] Decreasing the DE H-L in organicc ompounds has been attributed to extending p conjugation, [5] enhancing planarity, [6] or adding donor-acceptor motifs [7] to conjugated structures (see Scheme 1). [8] Despite the fact that the abovementioned concepts are all efficient in decreasing the DE H-L ,t here is still al ack of design concepts andasystematic framework to rationalize such concepts.T herefore, we aim to utilize the concept of structural distortion as at ool to modulate the DE H-L in pursuit of the rational design of intense NIR absorbingo rganic dyes. [8] Despite the fact that the abovementioned concepts are all efficient in decreasing the DE H-L ,t here is still al ack of design concepts andasystematic framework to rationalize such concepts.T herefore, we aim to utilize the concept of structural distortion as at ool to modulate the DE H-L in pursuit of the rational design of intense NIR absorbingo rganic dyes.…”

Section: Introductionmentioning

confidence: 99%

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Distortion‐Controlled Redshift of Organic Dye Molecules

Poater

Guerra

et al. 2020

Chemistry A European J

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It is shown,q uantum chemically,h ow structural distortion of an aromatic dye molecule can be leveraged to rationally tune its optoelectronic properties. By using a quantitative Kohn-Sham molecular orbital (KS-MO) approach,i nc ombinationw ith time-dependent DFT (TD-DFT), the influence of variouss tructurala nd electronic tuning parameters on the HOMO-LUMOg ap of ab enzenoid model dye have been investigated.T hese parameters include 1) out-of-plane bendingo ft he aromatic core,2 )bending of the bridge with respectt ot he core, 3) the nature of the bridge itself, and 4) p-p stacking. The study reveals the cou-pling of multiple structurald istortions as af unction of bridgel ength and number of bridges in benzene to be chiefly responsible for ad ecreased HOMO-LUMO gap, and consequently,r ed-shifting of the absorption wavelength associated with the lowest singlet excitation (l % 560 nm) in the model cyclophanes ystems. These physical insights togetherw ith ar ational approach for tuningt he oscillator strength were leveraged for the proof-of-concept design of an intense near-infrared( NIR) absorbing cyclophane dye at l = 785 nm. Thisd esign may contributet oanew class of distortion-controlled NIR absorbing organic dye molecules.Scheme1.Previousapproaches (top) [5][6][7] and our proposed distortion-controlled approach (bottom) for decreasing and tuning the HOMO-LUMOg ap in organic dye molecules. D = donor,A= acceptor.

Computationally Guided Molecular Design to Minimize the LE/CT Gap in D‐π‐A Fluorinated Triarylboranes for Efficient TADF via D and π‐Bridge Tuning

Rauch

Krebs

et al. 2020

Adv Funct Materials

In this combined experimental and theoretical study, a computational protocol is reported to predict the excited states in D‐π‐A compounds containing the B( F Xyl) 2 ( F Xyl = 2,6‐bis(trifluoromethyl)phenyl) acceptor group for the design of new thermally activated delayed fluorescence (TADF) emitters. To this end, the effect of different donor and π‐bridge moieties on the energy gaps between local and charge‐transfer singlet and triplet states is examined. To prove this computationally aided design concept, the D‐π‐B( F Xyl) 2 compounds 1 – 5 were synthesized and fully characterized. The photophysical properties of these compounds in various solvents, polymeric film, and in a frozen matrix were investigated in detail and show excellent agreement with the computationally obtained data. Furthermore, a simple structure–property relationship is presented on the basis of the molecular fragment orbitals of the donor and the π‐bridge, which minimize the relevant singlet–triplet gaps to achieve efficient TADF emitters.