Substituent-sensitive fluorescence of sequentially N-alkylated tetrabenzotetraaza[8]circulenes

Abstract

We explore the use of substituent-sensitive balance between fluorescence and non-radiative decay as a tool for optical tuning of promising materials for organic light emitting diode applications. A series of N-butylated tetrabenzotetraaza[8]circulenes are studied computationally in order to explain the gradual decrease of fluorescence intensity with the rise of the substituent number. The inter-system crossing probability is found to increase upon the gradual substitution of the circulene macrocycle as a result of a decrease of the S 1 -T 1 energy gap due to the deformation of the tetrabenzotetraaza[8]circulenes and thereby a distortion of the π-conjugation within the macrocycles. In contrast, the S 1 -T 1 spinorbit coupling matrix elements are quite insensitive to the number of outer substituents. As a result, the fluorescence-responsible ππ* transition becomes less intense and the fluorescence rate constant decreases.

Competition between the nonadiabatic electronic state-mixing and the Herzberg-Teller vibronic effects in fluorescence process of tetraoxa[8]circulene

“…Quantum chemical studies on the S1 state of 4B can be carried out without considering the nonadiabatic electronic state-mixing effect. This is probably true also for other hetero [8]circulenes, since previously calculated spectroscopic and photophysical properties are in good agreement with experimental data without accounting for the nonadiabatic electronic state-mixing effect [2,6,7,11,[16][17][18][30][31][32].…”

Calculating rate constants for intersystem crossing and internal conversion in the Franck–Condon and Herzberg–Teller approximations

“…We used this approximation in a previous work for calculating the k ISC rate constants for a number of organic and organometallic compounds. 4,12,33,34 However, this approximation cannot be employed for H 2 P. For 4B, the HT contribution to the rate constant for internal conversion (k IC−HT ) is one order of magnitude smaller than k IC−FC , whereas for PM567 k IC−HT ≈ k IC−FC .…”

Computational Studies of Aromatic and Photophysical Properties of Expanded Porphyrins

“…The same computational approach has also been successfully employed in calculations of rate constants for nonradiative electronic transitions in [8]circulene derivatives. [38][39][40] The aim of this work is to calculate rate constants for radiative and nonradiative electronic transitions between low-lying singlet and triplet states of expanded porphyrinoids. Calculations of magnetically induced current densities and current pathways provide additional information about relations between photophysical properties and the aromatic character of the studied molecules.…”