Solvent Effects on Cyanine Derivatives: A PCM Investigation

Double Hybrid Density Functionals for the Electronic Excitation Energies of Linear Cyanines

The lowest bright electronic excitations of seven model linear cyanines (CN3-CN15) using 28 double-hybrid (DH) density functionals are benchmarked against accurate and recent CC3 results. Some of these DH functionals are recently designed specifically for excited electronic state calculations. In addition, CIS, CIS(D), SCS-CIS(D), and SOS-CIS(D) were also tested. Four different basis sets were used for the vertical electronic excitation calculations: cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis. Augmented basis sets (e.g. aug-cc-pVDZ and aug-cc-pVTZ) are found to be required for accurate and consistent results using DH functionals. The DH functionals tested in this work are classified into four main groups: global double-hybrids (GDH), range-separated double-hybrids (RSDH), spin-component and spin-opposite scaling global double-hybrids (SCS/SOS-GDH), and spin-component and spin-opposite scaling range-separated double-hybrids (SCS/SOS-RSDH). Within these groups, the SCS/SOS-RSDH group of functionals is found to provide the lowest mean absolute error (MAE) values (in the range 0.020-0.148 eV) in comparison with the GDH group (0.195-0.441 eV), the RSDH group (0.186-0.511 eV), and the SCS/SOS-GDH group (0.079-0.461 eV). Of all the DH functionals and ab initio methods investigated in the present contribution, the following functionals are found to be the most accurate and consistent: SCS-ωB2GPPLYP (MAE = 0.036 eV), SOS-ωB2GPPLYP (MAE = 0.020 eV), SOS-ωB88PP86 (MAE = 0.035 eV), and SOS-ωPBEPP86 (MAE = 0.037 eV). In general, the ab initio methods tested here show mediocre performance as compared to many DH functionals.

Investigating the optical properties of BOIMPY dyes using ab initio tools

Using a computational approach combining Time-Dependent Density Functional Theory (TD-DFT) and second-order Coupled Cluster (CC2) approaches, we investigate the spectral properties of a large panel of BOIMPY dyes.

Calculations of BODIPY dyes in the ground and excited states using the M06-2X and PBE0 functionals

A number of fluorescent dyes based on BODIPY (4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene) have been studied theoretically. This paper presents the results of calculations of these BODIPY dyes in their ground and excited states, performed using DFT and TD-DFT methods, respectively. The influences of N,N-dimethylaminobenzyl, ortho-fluorophenol, and methyl substituents as well as the solvent polarity on the positions of the absorption and emission bands of the dyes were analyzed. The computational data obtained in this work were compared to the corresponding experimental data. The trends in the experimental data were found to agree with those shown by the computational data. Differences between the potential curves obtained when using linear-response (LR) and state-specific (SS) approaches for the ground and excited states are also reported. Graphical Abstract The article shows that the trends of the experimental dependencies λabs = f(Δf) and λem = f(Δf) well described by PBE0 (LR approach) and M06-2X (SS approach) calculations, respectively. The influence of substituents on the spectral characteristics of the BODIPY chromophore are analysed.

Investigating the properties of PODIPYs (phosphorus-dipyrromethene) with ab initio tools

What are the differences between BODIPYs and PODIPYs?

0-0 Energies Using Hybrid Schemes: Benchmarks of TD-DFT, CIS(D), ADC(2), CC2, and BSE/GW formalisms for 80 Real-Life Compounds

The 0-0 energies of 80 medium and large molecules have been computed with a large panel of theoretical formalisms. We have used an approach computationally tractable for large molecules, that is, the structural and vibrational parameters are obtained with TD-DFT, the solvent effects are accounted for with the PCM model, whereas the total and transition energies have been determined with TD-DFT and with five wave function approaches accounting for contributions from double excitations, namely, CIS(D), ADC(2), CC2, SCS-CC2, and SOS-CC2, as well as Green's function based BSE/GW approach. Atomic basis sets including diffuse functions have been systematically applied, and several variations of the PCM have been evaluated. Using solvent corrections obtained with corrected linear-response approach, we found that three schemes, namely, ADC(2), CC2, and BSE/GW allow one to reach a mean absolute deviation smaller than 0.15 eV compared to the measurements, the two former yielding slightly better correlation with experiments than the latter. CIS(D), SCS-CC2, and SOS-CC2 provide significantly larger deviations, though the latter approach delivers highly consistent transition energies. In addition, we show that (i) ADC(2) and CC2 values are extremely close to each other but for systems absorbing at low energies; (ii) the linear-response PCM scheme tends to overestimate solvation effects; and that (iii) the average impact of nonequilibrium correction on 0-0 energies is negligible.

Taking up the cyanine challenge with quantum tools

Cyanine derivatives, named from the Greek word kyanos meaning dark-blue, were discovered more than 150 years ago and remain one of the most widely used classes of organic dyes with contemporary applications in photography (panchromatic emulsions), information storage (CD-R and DVD-R media) and biochemistry (DNA and protein labeling) fields. Cyanine chromogens consist of a charged π-conjugated segment containing an odd number of sp(2) carbon atoms with the chain capped at the extremities by two electronegative centers, typically nitrogen or oxygen atoms. Cyanines are characterized by a vanishing bond length alternation indicating nearly equal carbon-carbon bond lengths, as well as a very intense and sharp absorption band presenting a shoulder. This hallmark band undergoes a strong red shift when the chain is extended. This so-called vinyl shift is extremely large (ca. 100 nm for each pair of carbon atoms added in the π-conjugated path), making cyanines ideal building blocks for the design of devices with near-infrared applications. Numerous cyanines also exhibit emission bands with large quantum yields. These exceptional optical properties explain why both canonical cyanines and the corresponding fluoroborates (e.g., boron-dipyrromethene, BODIPY) remain the focus of an ever-growing body of experimental work. In turn, this popularity has stimulated quantum mechanical investigations aiming, on the one hand, at probing the specific electronic nature of cyanine dyes and, on the other hand, at helping to design new dyes. However, the adiabatic approximation to time-dependent density functional theory, the most widespread ab initio model for electronically excited states, fails to accurately reproduce the absorption spectra of cyanine derivatives: it yields a systematic and large underestimation of the experimental wavelengths irrespective of the details of the computational protocol. In contrast, highly correlated wave function approaches provide accurate transition energies for model systems but are hardly applicable to real-life cyanines and BODIPY. This indicates that setting up a computationally tractable theoretical protocol that provides both robust and accurate optical spectra for cyanine-based dyes is a major challenge that has only been taken up lately. In this Account, we compile the most recent advances in the field by considering both compact streptocyanines and large fluoroborates. For the former, we summarize the key results obtained with a large panel of theoretical approaches, allowing us not only to understand the origin of the cyanine challenge but also to pinpoint the schemes presenting the most promising accuracy/effort ratio. For the latter, we show via selected examples how theoretical models can be used to reproduce simultaneously experimental band shapes and transition energies, thus paving the way to an efficient in silico design of new compounds.

Excited states of ladder-type π-conjugated dyes with a joint SOS-CIS(D) and PCM-TD-DFT approach

First-principle simulations aimed at accurately reproducing the excited state properties of a large series of ladder-type π-conjugated organic molecules containing heteroatoms (Si, S, B, O, and N) have been performed. In particular, time-dependent density functional theory (TD-DFT) calculations relying on several global and range-separated hybrid functionals have been carried out in conjunction with three variations of the polarizable continuum model (PCM), namely, the linear-response (LR), corrected linear-response (cLR), and state-specific (SS) approaches. For this series of molecules, similar to many borate derivatives, the cLR-PCM-TD-M06-2X approach can be used to reproduce the auxochromic effects that tune the 0-0 energies. However, TD-DFT yields rather large absolute deviations with respect to the experimental 0-0 energies. These systematic errors can be reduced by more than 0.1 eV when scaled opposite spin-configuration interaction singles with a double correction [SOS-CIS(D)] vertical calculations are combined to the PCM-TD-DFT results. This study demonstrates that such a "hybrid" scheme, where the geometrical and vibrational parameters, as well as the solvation effects, are determined with PCM-TD-DFT, whereas the transition energies are obtained with a wavefunction-based method, offers a useful compromise between accuracy and computational cost.

Spectroscopic signatures and structural motifs in isolated and hydrated serotonin: a computational study

The conformational landscapes of neutral serotonin characterized by MP2, CC2 and DFT methods. The Gph-out/anti conformation is found most stable.

The relationship between the boron dipyrromethene (BODIPY) structure and the effectiveness of homogeneous and heterogeneous solar hydrogen-generating systems as well as DSSCs

BODIPY photosensitizers were used to investigate the relationship between structure and effectiveness of visible-light-driven hydrogen production as well as DSSCs.

Effect of alkyl substituents in BODIPYs: a comparative DFT computational investigation

A detailed computational investigation encompassing the effects of alkyl groups on the structural and electronic properties of BODIPY dyes is presented.

Spectroscopic signatures and structural motifs in isolated and hydrated theophylline: a computational study

Optimized geometry of newly characterized theophylline dimer Form IV at MP2/6-311++G(d,p) level.

Full cLR-PCM calculations of the solvatochromic effects on emission energies

Are cLR-PCM excited-state geometries providing more accurate solvatochromic shifts?

Noble-metal-free BODIPY–cobaloxime photocatalysts for visible-light-driven hydrogen production

Four BODIPY–cobaloxime systems Co-Bn (n = 1–4) were studied as single-component homogeneous photocatalytic systems for H₂ generation in aqueous media.

Spectroscopic signatures and structural motifs in isolated and hydrated caffeine: a computational study

Blue and red shift of the VEE of the S₁ (¹ππ*) state of caffeine after forming complex with water at isolated and conjugated carbonyl site.