Unraveling the Room-Temperature Spin Dynamics of Photoexcited Pentacene in Its Lowest Triplet State at Zero Field

Abstract

Photo-excited pentacene, upon arriving via intersystem crossing into its lowest triplet state, has been extensively studied due to the large and relatively long-lived spin polarization that it exhibits. However, the spin dynamics of these triplets has not hitherto been accurately determined, with glaring inconsistencies between published values. Using zero-field transient electron paramagnetic resonance (ZF-trEPR), we here report the determination of a complete set of depopulation and spin-lattice relaxation rates for the lowest triplet state of pentacene doped at 0.1% into a p-terphenyl host crystal at room temperature in zero applied magnetic field. The rates of spin-lattice relaxation between the triplet's sublevels are found to be highly anisotropic (i.e. transition specific) and not negligible compared to the rates of depopulation from the same three sublevels back to pentacene's ground state. The spin dynamics as well as the ZF-trEPR technique reported here can aid the rational, quantitative engineering of applications such as room-temperature masers and triplet dynamic nuclear polarization (triplet-DNP).

Enhanced quantum sensing with room-temperature solid-state masers

“…B is the Einstein coefficient of the stimulated emission. The values of these parameters are adopted from previous studies on the pentacene's triplet spin system, where γ s = 4 × 10 4 s −1 taking both processes of depopulation and spin-lattice relaxation into account [39], B = 11 × 10 −8 s −1 and κ c = 2.1 × 10 6 s −1 are typical parameters of strontium titanate (STO)-based pentacene masers [40,41]. For simplicity, the model is solved in steady state, i.e.…”

Asymmetric N-heteroacene tetracene analogues as potential n-type semiconductors

“…1 OSCs are versatile materials that can be exploited as field-effect transistors (FETs), organic light emitting diodes (OLEDs) and more recently, microwave gain media in the form of masers. [2][3][4][5] Typical approaches to tuning the properties of OSCs towards these ends have involved modulation of the acene length, functionalisation of various C-H positions with inductive, mesomeric or electron withdrawing chemical groups or substitution of sp 2 carbon atoms with heteroatoms such as nitrogen, oxygen or sulfur. [6][7][8] Ultimately, the objective of these modifications is to modulate the functional properties by controlling the p-system topography and solid-state crystal packing -the latter of which can be exceedingly difficult to predict.…”

Invasive optical pumping for room-temperature masers, time-resolved EPR, triplet-DNP, and quantum engines exploiting strong coupling

“…Beyond its potential use as a low-noise preamplifier (LNA) for space communication [20] and magnetic resonance imaging [21], the P:TP maser also provides a convenient, low-cost platform for attaining the strong-coupling regime for investigating spin-based quantum phenomena [19]. An optically-pumped maser's performance is controlled by many factors including: (i) the quality factor Q and (ii) the magnetic mode volume V m of the microwave mode supported by its cavity, (iii) the magnetic filling factor of the maser crystal with respect to said mode, (iv) the power of the optical pumping scheme and finally, (v) the properties of the gain medium itself, such as its thermal stability and the various rates that control its spin dynamics [22].…”