Strong Duschinsky Mixing Induced Breakdown of Kasha’s Rule in an Organic Phosphor

Abstract

We present the novel observation that Duschinsky mixings can lead to the breakdown of Kasha’s rule in a white light phosphor molecule, dibenzo­[b,d]­thiophen-2-yl (4-chlorophenyl)­methanone. Our theoretical analyses show the energy gap between the T1 and T2 states (0.48 eV) is too large to allow for any significant population of the T2 state at room temperature and instead the faster intersystem crossing (ISC) between the S1 and T2 states is rather due to strong Duschinsky mixing, leading to the emission from the T2 state as well. A second-order cumulant-based method has been used for the calculation of the ISC rate, which suggests 2 orders of magnitude faster ISC rates for S1 → T2 compared to those for S1 → T1. We found that the carbonyl moiety of the S1 and T2 states of the molecule is significantly different with respect to bond angle and dihedral angles, engendering large displacements in selective normal modes, thus giving rise to strong Duschinsky mixing.

Single‐Component Molecular Dual Persistent Room Temperature Phosphorescence from Low‐ and High‐Lying Triplet States

“…For the latter mechanism, phosphorescence from the upper excited triplet state requires a large energy gap between two triplet excited states. [ 30 ] It is possible to achieve dual persistent RTP through the design of organic molecules with large T 1 and T 2 energy gaps. Additionally, to further achieve controllable phosphorescence from the different triplet excited states, the population of T 1 and T 2 states, which originate from two relatively independent pathways, is of utmost importance; they offer great opportunities for the regulation of the distribution of the triplet excitons.…”

Behind the scenes of spin-forbidden decay pathways in transition metal complexes

“…42 However, many instances of the breakdown of this rule has been documented. [43][44][45][46][47][48]48,49 Due to spin conservation, transition between different spin states is spin-forbidden and thus phosphorescence is usually much less intense compared to the spin-allowed counterpart. Pioneering works by Terenin, Lewis and Kasha, 50,51 led to the understanding of the electronic origin of molecular phosphorescence.…”

Demystifying the Origin of Vibrational Coherence Transfer Between the S1 and T1 States of the Pt-pop Complex

“…The expression for b is where Q denotes the dimensionless normal coordinates, and q 0 is the coordinate of the equilibrium geometry of the initial state. In addition, J and D indicate the Duschinsky rotation matrix − and displacement vector, respectively, which are connected through the relation Q T = JQ S + D , where Q S and Q T are the dimensionless normal coordinates of the singlet and triplet electronic states, respectively. Z = ∑ i e – βE i is the vibrational partition function of the initial electronic state and , where E i , T , and k represent the energy of the i th vibrational level, temperature, and Boltzmann constant, respectively.…”