Kinetics of Anti‐Kasha Photoreactions. Direct Excitation of a Higher Excited State

Abstract

Excited-state reactions (ESR) are of overwhelming importance in chemistry, physics and biology. Kinetics and steady-state characteristics of ESR are usually analyzed in the framework of the model, in which the first excited state of the initial form is populated. Due to the growing attention which is lately paid to the reactions excited through the energy levels higher than the first singlet level, we had developed new model of these reactions, describing the time characteristics of the normal form and the photoproduct populations. The system was excited via the higher S n singlet state. Generation of reaction product from both the first S 1 and S n excited states was studied. The model of arbitrary ESR was represented as a system of linear differential equations. Precise analytical solution was firstly obtained for the general case. Numerical analysis carried out on ESR parameters made it possible to reveal the role of reverse ESR, to estimates the S n state lifetime effect and the contribution of product formation due to the opening of its generation channel through the S n state. Data obtained theoretically was presented in graphical form which allowed a better understanding of the mechanisms of the photochemical processes and criteria for improving the efficiency of anti-Kasha processes.[a] Prof.

Computational Protocol To Predict Anti-Kasha Emissions: The Case of Azulene Derivatives

“…Therefore, in the latter cases, it might be difficult to track the underlying processes with time-resolved experimental techniques. 10 This is, for instance, the case of diphenyl polyenes, where emission from S 2 takes place as a consequence of the slow IC between S 2 and S 1 but also because of the thermal population of S 2 from S 1 . 11 Dual and multiple anti-Kasha scenarios have also been described for other systems.…”

“…Often, different mechanisms are possible and, in principle, one could fit the measured multiexponential decays considering different decay pathways and their kinetics. Therefore, in the latter cases, it might be difficult to track the underlying processes with time-resolved experimental techniques . This is, for instance, the case of diphenyl polyenes, where emission from S 2 takes place as a consequence of the slow IC between S 2 and S 1 but also because of the thermal population of S 2 from S 1 .…”

A Computational Protocol to Predict Anti-Kasha Emissions: The Case of Azulene Derivatives

“…Therefore, in the latter cases it might be difficult to track the underlying processes with time-resolved experimental techniques. 10 This is for instance the case of diphenyl polyenes, where emission from S 2 takes place as a consequence of the slow internal conversion between S 2 and S 1 but also because of the thermal population of S 2 from S 1 . 11 Dual and multiple anti-Kasha scenarios have also been described for other systems.…”

Theoretical Insights into Excited-State Intermolecular Proton Transfers of 2,7-Diazaindole in Water Using a Microsolvation Approach

“…Considering the shapes of frontier MOs of normal and tautomer forms (Figure S2 in the SI) for all 2,7-DAI­(H 2 O) n complexes, the electron densities of both the HOMO and LUMO are fully delocalized on the whole 2,7-DAI and no electron density is located around water molecules, attributed to the characteristics of the π → π* transition (S 0 –S 1 ) as the main electronic transition with the highest oscillator strength. Other transitions from lower states below the HOMO level to the LUMO level might be also involved in the ESInterPT process, as in the case of ESIntraPT systems. − Therefore, frontier MOs of the minor transition with oscillator strengths ( f ) of N, N*, and T* associating with the λ abs and λ emiss for all 2,7-DAI­(H 2 O) n complexes with the PCM model are listed in Table S3 in the SI. The minor transition with very low f less than 0.001 of all 2,7-DAI­(H 2 O) n complexes is assigned to HOMO–2 and LUMO, corresponding to n → π* character.…”