Unveiling the Photophysical Properties of Boron-dipyrromethene Dyes Using a New Accurate Excited State Coupled Cluster Method.

Romain Berraud-Pache,Giovanni Bistoni,Róbert Izsák,Frank Neese

doi:10.1021/acs.jctc.9b00559

Abstract

Boron-dipyrromethene (BODIPY) molecules form a class of fluorescent dyes known for their exceptional photoluminescence properties. Today, they are used extensively in various applications from fluorescent imaging to optoelectronics. The ease of altering the BODIPY core has allowed scientists to synthesize dozens of analogues by exploring chemical substitutions of various kinds or by increasing the length of conjugated groups. However, predicting the impact of any chemical change accurately is still a challenge, especially as most computational methods fail to describe correctly the photophysical properties of BODIPY derivatives. In this study, the recently developed coupled cluster method called "domain-based local pair natural orbital similarity transformed equation of motion-coupled cluster singles and doubles" (DLPNO-STEOM-CCSD) is employed to compute the lowest vertical excitation energies of more than 50 BODIPY molecules. The method performs remarkably well yielding an accuracy of about 0.06 eV compared to the experimental absorption maxima. We also provide an estimate to the error made by neglecting vibronic effects in the computed spectra. The dyes selected for investigation here span a large range of molecular sizes and chemical functionalities and are embedded in solvents with different polarities. We have also investigated if the method is able to correctly reproduce the impact of a single chemical modification on the absorption energy. To characterize the method in more specific terms, we have studied four large BODIPY analogues used in real-life applications due to their interesting chemical properties. These examples should illustrate the capacity of the DLPNO-STEOM-CCSD procedure to become a method of choice for the study of photophysical properties of medium to large organic compounds.

Highlights

Among the numerous fluorescent dyes that are presently in large-scale use, boron-dipyrromethene analogues[1,2] (BODIPY) play a main role
To test the accuracy of the domain-based local pair natural orbital (DLPNO)-STEOM-CCSD method, vertical excitation energies were calculated for all the BODIPY dyes from the work of Chibiani et al.[28] using several computational procedures
We began by estimating the effect of vibronic coupling and the basis set size and investigated the effect of the environment using a variety of models

Summary

INTRODUCTION

Among the numerous fluorescent dyes that are presently in large-scale use, boron-dipyrromethene analogues[1,2] (BODIPY) play a main role These compounds and their derivatives are found in many crucial applications like bioimaging, sensing and probes,[3,4] photodynamic therapy,[5−7] optoelectronics,[8] and photovoltaics.[9] BODIPY dyes exhibit some desirable photophysical properties such as large molecular absorption coefficients, a high fluorescent quantum yield, and the relative ease of adding substituents to the boron-dipyrromethene core. For each field of application described above, one representative BODIPY dye will be selected and studied with the newly implemented theoretical method

THEORETICAL ASPECTS AND COMPUTATIONAL DETAILS

RESULTS AND DISCUSSION

Comparing Vertical Excitation Energies to Band

CONCLUSIONS

■ REFERENCES