Disclosing Early Excited State Relaxation Events in Prototypical Linear Carbon Chains

Abstract

One-dimensional (1D) linear nanostructures comprising sp-hybridized carbon atoms, as derivatives of the prototypical allotrope known as carbyne, are predicted to possess outstanding mechanical, thermal, and electronic properties. Despite recent advances in their synthesis, their chemical and physical properties are still poorly understood. Here, we investigate the photophysics of a prototypical polyyne (i.e., 1D chain with alternating single and triple carbon bonds) as the simplest model of finite carbon wire and as a prototype of spcarbon-based chains. We perform transient absorption experiments with high temporal resolution (<30 fs) on monodispersed hydrogen-capped hexayne H�(C�C) 6 �H synthesized by laser ablation in liquid. With the support of computational studies based on ground state density functional theory (DFT) and excited state time-dependent (TD)-DFT calculations, we provide a comprehensive description of the excited state relaxation processes at early times following photoexcitation. We show that the internal conversion from a bright highenergy singlet excited state to a low-lying singlet dark state is ultrafast and takes place with a 200 fs time constant, followed by thermalization on the picosecond time scale and decay of the low-energy singlet state with hundreds of picoseconds time constant. We also show that the time scale of these processes does not depend on the end groups capping the sp-carbon chain. The understanding of the primary photoinduced events in polyynes is of key importance both for fundamental knowledge and for potential optoelectronic and light-harvesting applications of low-dimensional nanostructured carbon-based materials.

Torsional Disorder in Tetraphenyl [3]-Cumulenes: Insight into Excited State Quenching

“…Photochem 2024, 4 139 Despite this interest, reports investigating the excited state dynamics and photochemistry of cumulenes are scarce [23][24][25][26]. Earlier reports investigating the optical properties of [3]-cumulenes functionalized with phenyl groups demonstrated that ground-state energy is significantly perturbed by small changes to the phenyl group's torsional angle [27][28][29].…”

“…Photochem 2024, 4, FOR PEER REVIEW 2 observed, suggesting further scopes to extend the uses of cumulenes for exciton multiplication via singlet fission or other triplet-based catalytic pathways [19][20][21][22]. Despite this interest, reports investigating the excited state dynamics and photochemistry of cumulenes are scarce [23][24][25][26]. Earlier reports investigating the optical properties of [3]-cumulenes functionalized with phenyl groups demonstrated that groundstate energy is significantly perturbed by small changes to the phenyl groupʹs torsional angle [27][28][29].…”