The role of vibronic coupling in the electronic spectroscopy of maleimide: a multi-mode and multi-state quantum dynamics study

Abstract

The first two excitation bands below 7 eV in the electronic absorption spectrum of maleimide are investigated using a model Hamiltonian including four low-lying singlet excited states within the manifold...

Intramolecular thiomaleimide [2 + 2] photocycloadditions: stereoselective control for disulfide stapling and observation of excited state intermediates by transient absorption spectroscopy

“…Based on literature precedent and ab initio calculations, we proposed a likely mechanism upon photoexcitation at 354 nm, chosen as it is the rst dominant absorption band in the reactants' UV spectra (Scheme 4, shown as a suggested mechanism for the dimerisation of thiomaleimide 1). 35,[37][38][39] Ab initio calculations conrmed the 354 nm band belongs to S 2 (p 1 p*) (see ESI Table 4 †), thus we anticipated an initial p / p* electronic transition to form the S 2 (p 1 p*) state. A recent report by Worth and coworkers indicates that the lowest pp* excited state in maleimide undergoes rapid internal conversion (IC) to the lowest Table 1 The measured quantum yield F of [2 + 2] photocycloaddition for the different maleimides at a range of concentrations in MeCN (unless otherwise stated), along with their initial rates of reactant use.…”

“…36 The initial rates for the maleimides were calculated from the gradient of the concentration vs. time graph up to $10% conversion (see ESI Fig. 13 np* excited state, 35 and thus a similar S 2 (p 1 p*) / S 1 (n 1 p*) IC was expected for thiomaleimides. The subsequent mechanism for [2 + 2] photocycloaddition is based on the widely described reaction mechanism for a,b-unsaturated carbonyls.…”

“…Another key difference is the shi of the major C]O stretch from Scheme 4 Hypothesised mechanism for the [2 + 2] photocycloaddition reaction. 35,[37][38][39] Fig. 2 Static UV spectra for (a) thiomaleimide 1 and photoproduct 2 (0.1 mM) and (b) bis-thiomaleimide 4a and photoproduct 5a (0.05 mM).…”

“…For both thiomaleimide 1 and maleimide 8 , the first band in the spectra with a significant absorption is associated with a transition to form the lowest state (from hereon, will be referred to as π* for convenience), confirmed by ab initio calculations performed on maleimide 8 (ref. 32–35) and a model thiomaleimide chromophore (see ESI Table 4 and ESI Fig. 10†).…”

A Fragment Diabatization Linear Vibronic Coupling Model for Quantum Dynamics of Multichromophoric Systems: Population of the Charge Transfer State in the Photoexcited Guanine Cytosine Pair

“…Several strategies may be employed to ameliorate these deficiencies, such as moving to a quadratic vibronic coupling model (or at least some quadratic corrections like done in Refs. 16,71,77), fitting with non-harmonic functions when anharmonicity is confined to a few degrees of freedom, and mixed quantum classical approaches to deal with large amplitude motions. 78 Such developments fall, however, outside the aim of the present contribution and will be tackled in future studies.…”