Ultrafast and long-time excited state kinetics of an NIR-emissive vanadium(iii) complex I: synthesis,spectroscopy and static quantum chemistry

In spite of intense, recent research efforts, luminescent transition metal complexes with Earth-abundant metals are still very rare owing to the small ligand field splitting of 3d transition metal complexes and the resulting non-emissive low-energy metal-centered states. Low-energy excited states decay efficiently non-radiatively, so that near-infrared emissive transition metal complexes with 3d transition metals are even more challenging. We report that the heteroleptic pseudo-octahedral d²-vanadium(iii) complex VCl₃(ddpd) (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-yl-pyridine-2,6-diamine) shows near-infrared singlet → triplet spin–flip phosphorescence maxima at 1102, 1219 and 1256 nm with a lifetime of 0.5 μs at room temperature. Band splitting, ligand deuteration, excitation energy and temperature effects on the excited state dynamics will be discussed on slow and fast timescales using Raman, static and time-resolved photoluminescence, step-scan FTIR and fs-UV pump-vis probe spectroscopy as well as photolysis experiments in combination with static quantum chemical calculations. These results inform future design strategies for molecular materials of Earth-abundant metal ions exhibiting spin–flip luminescence and photoinduced metal–ligand bond homolysis.

Vanadium is an abundant and cheap metal but near-infrared luminescent vanadium complexes are extremely rare with largely unexplored photophysics and photochemistry. We delineate the photodynamics of VCl₃(ddpd) to infer novel design strategies.     

Ultrafast excited state dynamics of Pt(II) chromophores bearing multiple infrared absorbers

The paper reports the synthesis, structural characterization, electrochemistry, ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopy associated with two independent d (8) square planar Pt(II) diimine chromophores, Pt(dnpebpy)Cl 2 ( 1) and Pt(dnpebpy)(C[triple bond]Cnaph) 2 ( 2), where dnpebpy = 4,4'-(CO 2CH 2- (t) Bu) 2-2,2'-bipyridine and CCnaph = naphthylacetylide. The neopentyl ester substitutions provided markedly improved complex solubility relative to the corresponding ethyl ester which facilitates synthetic elaboration as well as spectroscopic investigations. Following 400 nm pulsed laser excitation in CH 2Cl 2, the 23 cm (-1) red shift in the nu C=O vibrations in 1 are representative of a complex displaying a lowest charge-transfer-to-diimine (CT) excited state. The decay kinetics in 1 are composed of two time constants assigned to vibrational cooling of the (3)CT excited-state concomitant with its decay to the ground state (tau = 2.2 +/- 0.4 ps), and to cooling of the formed vibrationally hot ground electronic state (tau = 15.5 +/- 4.0 ps); we note that an assignment of the latter to a ligand field state cannot be excluded. Ultrafast TA data quantitatively support these assignments yielding an excited-state lifetime of 2.7 +/- 0.4 ps for the (3)CT excited-state of 1 and could not detect any longer-lived species. The primary intention of this study was to develop a Pt (II) complex ( 2) bearing dual infrared spectroscopic tags (C[triple bond]C attached to the metal and CO (ester) attached to the diimine ligand) to independently track the movement of charge density in different segments of the molecule following pulsed light excitation. Femtosecond laser excitation of 2 in CH 2Cl 2 at 400 nm simultaneously induces a red-shift in both the nu C=O (-30 cm (-1)) and the nu C[triple bond]C (-61 cm (-1)) vibrations. The TRIR data in 2 are consistent with a charge transfer assignment, and the significant decrease of the energy of the nu C[triple bond]C vibration suggests a considerable contribution from the acetylide ligands in the highest occupied molecular orbital. Therefore, we assign the lowest energy optical transitions in 2 as a combination of metal-to-ligand and ligand-to-ligand charge transfers. The excited-state of 2 is emissive at RT, with an emission maximum at 715 nm, quantum yield of 0.0012, and lifetime of 23 ns.     

Ultrafast excited-state excitation dynamics in a quasi-two-dimensional light-harvesting antenna based on ruthenium(II) and palladium(II) chromophores

A detailed study on the excited-state-excitation migration taking place within the tetranuclear complex [{(tbbpy)(2)Ru(tmbi)}(2){Pd(allyl)}(2)](PF(6))(2) (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine and tmbi = 5,6,5',6'-tetramethyl-2,2'-bibenzimidazolate) is presented. The charge transfer is initiated by the photoexcitation into the lowest metal-to-ligand charge-transfer (MLCT) band of one of the peripheral ruthenium(II) chromophores and terminates on the central structurally complex Pd(2) (II)(allyl)(2) subunit. Thus, the system under investigation can be thought of as a functional model for the photosynthesis reaction center in plants. The kinetic steps involved in the overall process are inferred from femtosecond time-resolved transient-grating kinetics recorded at spectral positions within the regions of ground-state bleach and transient absorption. The kinetics features a complex non-exponential time behavior and can be fitted to a bi-exponential rise (tau(1)> or =200 fs, tau(2) approximately 1.5 ps) and a mono- or bi-exponential decay, depending on the experimental situation. The data leads to the formulation of a model for the intramolecular excitation-hopping ascribing intersystem crossing and subsequent cooling as the two fastest observed processes. Following these initial steps, charge transfer from the ruthenium to the central complex Pd(2)(allyl)(2) moiety is observed with a characteristic time constant of 50 ps. A 220-ps component that is observed in the ground-state recovery only is attributed to excitation equilibration between the two identical Pd(allyl) chromophores.     

Ultrafast twisting dynamics in the excited state of auramine

Relaxation dynamics of the excited state of bis-[4-(dimethylamino)-phenyl] methaniminium chloride (Auramine) has been investigated using subpicosecond time-resolved absorption spectroscopic technique in both aprotic and alcoholic solvents. The locally excited (LE) state, formed following photoexcitation of Auramine using 400 nm light, undergoes intramolecular charge transfer (ICT) process, which is accompanied by the twisting of the dimethylanilino groups. Time evolution of the transient absorption-stimulated emission spectra as well as the wavelength dependence of the temporal dynamics investigated in each kind of solvents suggest that the relaxation process proceeds via the formation of at least two transient states (TS I and TS II), which are geometrical conformers and consecutively formed following the decay of the LE state. Twisting of the dimethylaniline groups are nearly barrierless processes, the rates of which show linear correlation both with the macroscopic or shear viscosities as well as the solvation times of the solvents. Time-dependent and fractional viscosity dependence of the relaxation rates of the LE and the TS I states in aprotic solvents suggest the multidimensionality of the reaction coordinate as well as reveal the viscoelastic property of the solvents. However, in normal alcohols, in addition to these two factors, activation energy of the solvent viscosity may be another important factor for the slower twisting dynamics of Auramine in alcohols. To explain the viscosity dependence of the decay time of the TS II state, which undergoes an efficient internal conversion process to the ground state, the possibility of occurrence of different mechanisms, such as, energy gap law, involvement of intramolecular high frequency modes, as well as the phenyl group twisting motion on a potential energy surface having a photochemical funnel, have been discussed. TDDFT method has been applied to obtain the optimized electronic structures of the transient states but it has been possible to obtain only that for the TS II state.     

Ultrafast excited state dynamics of modified phthalocyanines: p-HPcZn and p-HPcCo

Two modified metallophthalocyanines (MPcs) containing sulfonic naphthoxy substituents were synthesized. The measurements of transient absorption and time-resolved photoluminescence were used to study the ultrafast response and excited state dynamics of two MPcs in dimethyl sulfoxide (DMSO) solution, which were predominantly in the monomeric form. Under excitation at 400 nm, these molecules experience vibrational relaxation to the bottom of the first excited state and then the excitation rapidly converts to the low-lying charge-transfer (CT) state and finally reaches the triplet states. Under excitation at 800 nm, they show a two-photon absorption character, and their excited state dynamics exhibit strong dependence on the probe wavelength. The main results with 400 nm pumping are similar to the results with 800 nm pumping. For p-HPcZn, weak two-photon photoluminescence was also observed with a lifetime of 52 +/- 2 ps. A four-level model was used to illustrate the excited state dynamics of p-HPcZn, while a five-level model was suggested for p-HPcCo molecule.     

Ultrafast fluorescence detection in tris(2,2'-bipyridine)ruthenium(II) complex in solution: relaxation dynamics involving higher excited states

The excited-state dynamics of a transition metal complex, tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)(3)](2+), has been investigated using femtosecond fluorescence upconversion spectroscopy. The relaxation dynamics in these molecules is of great importance in understanding the various ultrafast processes related to interfacial electron transfer, especially in semiconductor nanoparticles. Despite several experimental and theoretical efforts, direct observation of a Franck-Condon singlet excited state in this molecule was missing. In this study, emission from the Franck-Condon excited singlet state of [Ru(bpy)(3)](2+) has been observed for the first time, and its lifetime has been estimated to be 40 +/- 15 fs. Biexponential decays with a fast rise component observed at longer wavelengths indicated the existence of more than one emitting state in the system. From a detailed data analysis, it has been proposed that, on excitation at 410 nm, crossover from higher excited (1)(MLCT) states to the vibrationally hot triplet manifold occurs with an intersystem crossing time constant of 40 +/- 15 fs. Mixing of the higher levels in the triplet state with the singlet state due to strong spin-orbit coupling is proposed. This enhances the radiative rate constant, k(r), of the vibrationally hot states within the triplet manifold, facilitating the upconversion of the emitted photons. The vibrationally excited triplet, which is emissive, undergoes vibrational cooling with a decay time in the range of 0.56-1.3 ps and relaxes to the long-lived triplet state. The results on the relaxation dynamics of the higher excited states in [Ru(bpy)(3)](2+) are valuable in explaining the role of nonequilibrated higher excited sensitizer states of transition metal complexes in the electron injection and other ultrafast processes.     

Ultrafast excited-state dynamics in vitamin B12 and related cob(III)alamins

Femtosecond transient IR and visible absorption spectroscopies have been employed to investigate the excited-state photophysics of vitamin B12 (cyanocobalamin, CNCbl) and the related cob(III)alamins, azidocobalamin (N3Cbl), and aquocobalamin (H2OCbl). Excitation of CNCbl, H2OCbl, or N3Cbl results in rapid formation of a short-lived excited state followed by ground-state recovery on time scales ranging from a few picoseconds to a few tens of picoseconds. The lifetime of the intermediate state is influenced by the sigma-donating ability of the axial ligand, decreasing in the order CNCbl > N3Cbl > H2OCbl, and by the polarity of the solvent, decreasing with increasing solvent polarity. The peak of the excited-state visible absorption spectrum is shifted to ca. 490 nm, and the shape of the spectrum is characteristic of weak axial ligands, similar to those observed for cob(II)alamin, base-off cobalamins, or cobinamides. Transient IR spectra of the upper CN and N3 ligands are red-shifted 20-30 cm(-1) from the ground-state frequencies, consistent with a weakened Co-upper ligand bond. These results suggest that the transient intermediate state can be attributed to a corrin ring pi to Co 3d(z2) ligand to metal charge transfer (LMCT) state. In this state bonds between the cobalt and the axial ligands are weakened and lengthened with respect to the corresponding ground states.     

Ultrafast intermolecular hydrogen bond dynamics in the excited state of fluorenone

Steady-state fluorescence and time-resolved absorption measurements in pico- and femtosecond time domain have been used to investigate the dynamics of hydrogen bond in the excited singlet (S(1)) state of fluorenone in alcoholic solvents. A comparison of the features of the steady-state fluorescence spectra of fluorenone in various kinds of media demonstrates that two spectroscopically distinct forms of fluorenone in the S(1) state, namely the non-hydrogen-bonded (or free) molecule as well as the hydrogen-bonded complex, are responsible for the dual-fluorescence behavior of fluorenone in solutions of normal alcoholic solvents at room temperature (298 K). However, in 2,2,2-trifluoroethanol (TFE), a strong hydrogen bond donating solvent, emission from only the hydrogen-bonded complex is observed. Significant differences have also been observed in the temporal evolution of the absorption spectroscopic properties of the S(1) state of fluorenone in protic and aprotic solvents following photoexcitation using 400 nm laser pulses. An ultrafast component representing the solvent-induced vibrational energy relaxation (VER) process has been associated with the dynamics of the S(1) state of fluorenone in all kinds of solvents. However, in protic solvents, in addition to the VER process, further evolution of the spectroscopic and dynamical properties of the S(1) state have been observed because of repositioning of the hydrogen bonds around the carbonyl group. In normal alcohols, two different kinds of hydrogen-bonded complex of the fluorenone-alcohol system with different orientations of the hydrogen bond with respect to the carbonyl group and the molecular plane of fluorenone have been predicted. On the other hand, in TFE, formation of only one kind of hydrogen-bonded complex has been observed. These observations have been supported by theoretical calculations of the geometries of the hydrogen-bonded complexes in the ground and the excited states of fluorenone. Linear correlation between the lifetimes of the equilibration process occurring because of repositioning of the hydrogen bonds and Debye or longitudinal relaxation times of the normal alcoholic solvents establish the fact that, in weakly hydrogen bond donating solvents, the hydrogen bond dynamics can be described as merely a solvation process. Whereas, in TFE, hydrogen bond dynamics is better described by a process of conversion between two distinct excited states, namely, the non-hydrogen-bonded form and the hydrogen-bonded complex.     

Ultrafast dynamics and excited state deactivation of [Ru(bpy)2Sq]+ and its derivatives

Femtosecond transient absorption spectroscopy has been employed to understand the excited state dynamics of [Ru(bpy)(2)Sq](+) (I; bpy is 2,2'-bipyridyl, and Sq is the deprotonated species of the semiquinone form of 1,2-dihydroxy benzene) and its derivatives, a widely studied near-infrared (NIR) active electrochromic dye. Apart from the well-defined dpi(Ru) --> pi(bpy)-based metal-to-ligand charge transfer (MLCT) transition bands at approximately 480 nm, this class of molecules generally shows another dpi(Ru) --> pi(Sq)(SOMO)-based intense MLCT band at around 900 nm, which is known to be redox active and bleaches reversibly upon a change in the oxidation state of the coordinated dioxolene moiety. To have better insight into the photoinduced electron transfer dynamics associated with this MLCT transition, detailed investigations have been carried out on exciting this MLCT band at 800 nm. Immediately after photoexcitation, bleach at 900 nm has been observed, whose recovery is found to follow a triexponential function with major contribution from the ultrafast component. This ultrafast component of approximately 220 fs has been ascribed to the S(1) to S(0) internal conversion process. In addition to the bleach, we have detected two transient species absorbing at 730 and 1000 nm with a formation time approximately 220 fs for both species. The excited state lifetimes for these two transient species have been measured to be 1.5 and 11 ps and have been attributed to excited singlet ((1)MLCT) and triplet ((3)MLCT) states, respectively. Transient measurements carried out on the different but analogous derivatives (II and III) have also shown similar recovery dynamics except that the rate for the internal conversion process has increased with the decrease in the S(1) to S(0) energy gap. The observed results are consistent with the energy gap law for nonradiative decay from S(1) to S(0).     

Synthesis, excited-state dynamics, and reactivity of a directly-linked pyromellitimide-(porphinato)zinc(II) complex

N-[5-(10,20-Diphenylporphinato)zinc(II)]-N'-(octyl)pyromellitic diimide (PZn-PI), a meso-pyromellitimide-substituted (porphinato)zinc(II) compound, has been fabricated from the reaction of (5-amino-10,20-diphenylporphinato)zinc(II) with pyromellitic dianhydride in the presence of octylamine. Interrogation of the photoinduced charge separation (CS) and thermal charge recombination (CR) electron-transfer (ET) dynamics for PZn-PI in CH(2)Cl(2) via pump-probe transient absorption spectroscopic methods shows that tau(CS) and tau(CR) are 770 and 5200 fs, respectively. These ET dynamics differ from those elucidated previously for closely related 5-quinonyl-substituted (porphinato)metal compounds, and derive from the fact that the low-lying excited states for PZn-PI are porphyrin-localized, possessing little charge-transfer character. The synthesis of N-(5-[15-(2-(triisopropylsilyl)ethynyl)-10,20-diphenylporphinato]zinc(II))-N'-(octyl)pyromellitic diimide demonstrates that PZn-PI can be halogenated at its 15-meso-position and used subsequently as a substrate in metal-catalyzed cross-coupling reactions; the reactivity of PZn-PI is unusual with respect to many directly linked donor-acceptor compounds in that it is stable to these oxidizing and reducing reaction conditions.     

Ultrafast excited state dynamics of fucoxanthin: excitation energy dependent intramolecular charge transfer dynamics

Carotenoids containing a carbonyl group in conjugation with their polyene backbone are naturally-occurring pigments in marine organisms and are essential to the photosynthetic light-harvesting function in aquatic algae. These carotenoids exhibit spectral characteristics attributed to an intramolecular charge transfer (ICT) state that arise in polar solvents due to the presence of the carbonyl group. Here, we report the spectroscopic properties of the carbonyl carotenoid fucoxanthin in polar (methanol) and nonpolar (cyclohexane) solvents studied by steady-state absorption and femtosecond pump-probe measurements. Transient absorption associated with the optically forbidden S(1) (2(1)A) state and/or the ICT state were observed following one-photon excitation to the optically allowed S(2) (1(1)B) state in methanol. The transient absorption measurements carried out in methanol showed that the ratio of the ICT-to-S(1) state formation increased with decreasing excitation energy. We also showed that the ICT character was clearly visible in the steady-state absorption in methanol based on a Franck-Condon analysis. The results suggest that two spectroscopic forms of fucoxanthin, blue and red, exist in the polar environment.     

Ultrafast excited state relaxation dynamics of branched donor-pi-acceptor chromophore: evidence of a charge-delocalized state

Excited-state dynamics and complete transient absorption features of the trimer tris-4,4',4' '-(4-nitrophenyleethynyl)triphenylamine and the monomer 4-N,N-(dimethylamino)-4'-nitrotolane have been obtained from femtosecond pump-probe spectroscopy. The measurements are carried out to understand the mechanism behind enhanced two-photon absorption cross-sections of branched systems over their linear counterparts. Absorption and emission transition dipole moments of monomer and trimer in toluene have suggested that the emitting state of trimer is different from the monomer and probably is arising from the charge-delocalized C(3) symmetry state. Ultrafast transient absorption measurements on these molecules have spectroscopically validated the presence of an initial electron delocalized state with the C(3) symmetry state in the trimer molecule. The results have shown that there is a slower rate of internal conversion from the C(3) symmetry state to intramolecular charge transfer of trimer suggesting a barrier between them. Also, presence of a charge-stabilized state and involvement of a nonemissive state in the excited-state deactivation has been observed for both monomer and trimer.     

Ground- and excited-state electronic structure of an emissive pyrazine-bridged ruthenium(II) dinuclear complex

The synthesis, characterization, and electrochemical, photophysical, and photochemical properties of the binuclear compounds [(Ru(H8-bpy)2)2((Metr)2Pz)](PF6)2 (1) and [(Ru(D8-bpy)2)2((Metr)2Pz)](PF6)2 (2), where bpy is 2,2'-bipyridine and H2(Metr)2Pz is the planar ligand 2,5-bis(5'-methyl-4'H-[1,2,4]triaz-3'-yl)pyrazine, are reported. Electrochemical and spectro-electrochemical investigations indicate that the ground-state interaction between each metal center is predominantly electrostatic and in the mixed-valence form only a low level of ground-state delocalization is present. Resonance Raman, transient, and time-resolved spectroscopies enable a detailed assignment to be made of the excited-state photophysical properties of the complexes. Deuteriation is employed to both facilitate spectroscopic characterization and investigate the nature of the lowest excited states.     

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures

Many of the spectroscopic features and photophysical properties of carotenoids are explained using a three-state model in which the strong visible absorption of the molecules is associated with an S0 (1(1)Ag-) --> S2 (1(1)Bu+) transition, and the lowest lying singlet state, S1 (2(1)Ag-), is a state into which absorption from the ground state is forbidden by symmetry. However, semiempirical and ab initio quantum calculations have suggested additional excited singlet states may lie either between or in the vicinity of S1 (2(1)Ag-) and S2 (1(1)Bu+), and some ultrafast spectroscopic studies have reported evidence for these states. One such state, denoted S*, has been implicated as an intermediate in the depopulation of S2 (1(1)Bu+) and as a pathway for the formation of carotenoid triplet states in light-harvesting complexes. In this work, we present the results of an ultrafast, time-resolved spectroscopic investigation of a series of open-chain carotenoids derived from photosynthetic bacteria and systematically increasing in their number of pi-electron carbon-carbon double bonds (n). The molecules are neurosporene (n = 9), spheroidene (n = 10), rhodopin glucoside (n = 11), rhodovibrin (n = 12), and spirilloxanthin (n = 13). The molecules were studied in acetone and CS2 solvents at room temperature. These experiments explore the effect of solvent polarity and polarizability on the spectroscopic and kinetic behavior of the molecules. The molecules were also studied in ether/isopentane/ethanol (EPA) glasses at 77 K, in which the spectral resolution is greatly enhanced. Analysis of the data using global fitting techniques has revealed the ultrafast dynamics of the excited states and spectral changes associated with their decay, including spectroscopic features not previously reported. The data are consistent with S* being identified with a twisted conformational structure, the yield of which is increased in molecules having longer pi-electron conjugations. In particular, for the longest molecule in the series, spirilloxanthin, the experiments and a detailed quantum computational analysis reveal the presence of two S* states associated with relaxed S1 (2(1)Ag-) conformations involving nearly planar 6-s-cis and 6-s-trans geometries. We propose that in polar solvents, the ground state of spirilloxanthin takes on a corkscrew conformation that generates a net solute dipole moment while decreasing the cavity formation energy. Upon excitation and relaxation into the S1 (2(1)Ag-) state, the polyene unravels and flattens into a more planar geometry with comparable populations of 6-s-trans and 6-s-cis conformations.     

Solvent-induced configuration mixing and triplet excited state inversion exemplified in a Pt(II) complex

The present study provides clear-cut experimental evidence for solvent-induced configuration mixing and complete triplet state inversion at room temperature in a Pt(ii) charge transfer complex bearing a combination of energetically proximate charge transfer and intraligand triplet excited states.     

Ultrafast dynamics of cyclohexene and cyclohexene-d10 excited at 200 nm.

By exciting cyclohexene in the gas phase at 200 nm and probing it by nonresonant multiphoton ionization with mass-selective detection of the ion yields, we found four time constants tau(i) (20, 47, 43, 350 fs). Whereas deuteration lengthens tau2 by a factor of 1.4, the other constants do not change. Tau1-tau3 represent traveling times through observation windows on excited surfaces, whereas tau4 reflects a process in the hot ground state. We assign tau1 (20 fs) to departure from the Franck-Condon regions of the Rydberg and pipi* states, which are both populated at 200 nm, and tau2 (47 fs) to traveling along the pipi* surface and suggest that a [1,3]-sigmatropic H shift begins in this state. This rationalizes the deuterium effect on tau2. To explain why this window is followed by a process not subject to a D effect, we postulate that the pipi surface is crossed late (i.e., at low energy) by the zwitterionic state Z and that formation of a carbene (the known photochemical product, cyclopentylcarbene) begins there. The corresponding 1,2-shift of a CC bond is then (within tau4 = 350 fs) largely reversed on the ground-state surface, while a smaller part of the carbene forms products such as methylenecyclopentane within the same time. Carbene formation is probably accompanied by some cis-trans isomerization. The wavelength dependence of carbene formation is attributed to a memory for the initially excited state, based on momentum conservation. The processes are most likely typical of simple olefins. The fragmentation pattern showed that butadiene is not formed until at least 500 ps. The retro-Diels-Alder reaction, known to take place in the ground state, thus only occurs later.     

Preferential solvation of an ILCT excited state in bis(terpyridine-phenylene-vinylene) Zn(II) complexes

The excited state of terpyridine derivatives of phenylene-vinylene fragments chelating Zn(II) show a strong solvatochromism (up to 56 nm) upon preferential solvation by polar solvents of an intraligand charge transfer state.     

Ultrafast singlet excited-state polarization in electronically asymmetric ethyne-bridged bis[(porphinato)zinc(II)] complexes

The excited-state dynamics of two conjugated bis[(porphinato)zinc(II)] (bis[PZn]) species, bis[(5,5'-10,20-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenyl]porphinato)zinc(II)]ethyne (DD) and [(5,-10,20-bis[3,5-bis(3,3-dimethyl-1-butyloxy)phenyl]porphinato)zinc(II)]-[(5',-15'-ethynyl-10',20'-bis(heptafluoropropyl)porphinato)zinc(II)]ethyne (DA), were studied by pump-probe transient absorption spectroscopy and hole burning techniques. Both of these meso-to-meso ethyne-bridged bis[PZn] compounds display intense near-infrared (NIR) transient S(1)-->S(n) absorptions and fast relaxation of their initially prepared, electronically excited Q states. Solvational and conformational relaxation play key roles in both DD and DA ground- and excited-state dynamics; in addition to these processes that drive spectral diffusion, electronically excited DA manifests a 3-fold diminution of S(1)-->S(0) oscillator strength on a 2-20 ps time scale. Both DD and DA display ground-state and time-dependent excited-state conformational heterogeneity; hole burning experiments show that this conformational heterogeneity is reflected largely by the extent of porphyrin-porphyrin conjugation, which varies as a function of the pigment-pigment dihedral angle distribution. While spectral diffusion can be seen for both compounds, rotational dynamics driving configurational averaging (tau approximately 30 ps), along with a small solvational contribution, account for essentially all of the spectral changes observed for electronically excited DD. For DA, supplementary relaxation processes play key roles in the excited-state dynamics. Two fast solvational components (0.27 and 1.7 ps) increase the DA excited-state dipole moment and reduce concomitantly the corresponding S(1)-->S(0) transition oscillator strength; these data show that these effects derive from a time-dependent change of the degree of DA S(1)-state polarization, which is stimulated by solvation and enhanced excited-state inner-sphere structural relaxation.