Adjunctive fixation of the humeral epicondyle in a lateral condylar fracture model: Ex vivo comparison of pins and plates with a novel composite (AdhFix).

OBJECTIVE: To compare the biomechanical properties of using a novel composite construct (AdhFix) to an interfragmentary Kirschner wire or a reconstruction plate as adjunctive epicondylar stabilization in simulated lateral unicondylar humeral fractures. STUDY DESIGN: Cadaveric biomechanical assessment. SAMPLE POPULATION: Paired humeri harvested from skeletally mature dogs (14-41 kg), nine cadavers per group. METHODS: Simulated lateral unicondylar humeral fractures were stabilized with a transcondylar 4.5 mm cortical screw placed in lag fashion. Adjunct fixations consisting of a novel composite incorporating 2.7 mm cortical screws on one side, and either a 2.7 mm reconstruction plate or a 1.6 mm Kirschner wire on the contralateral side, were tested within paired humeri. Repaired humeri were axially loaded to failure and construct stiffness, yield load, and ultimate load were obtained from the load-deformation curves. RESULTS: In pairwise comparison, yield load was significantly higher for AdhFix group compared to the pin group, p = .016. No statistical significance was seen in the comparison between AdhFix group and the plate group, p = .25. CONCLUSION: Adhfix was mechanically superior to K-wires, and comparable to plate fixation, for adjunctive fixation in a lateral humeral condylar model. Our results support further investigation of the novel composite for adjunct fracture fixation in lateral humeral condylar fractures. CLINICAL SIGNIFICANCE: The novel composite tested may be a viable alternative for adjunct fixation of humeral condylar fractures, a technique that circumvents plate contouring.

Rationalisation of Antifungal Properties of α-Helical Pore-Forming Peptide, Mastoparan B.

The high mortality associated with invasive fungal infections, narrow spectrum of available antifungals, and increasing evolution of antifungal resistance necessitate the development of alternative therapies. Host defense peptides are regarded as the first line of defense against microbial invasion in both vertebrates and invertebrates. In this work, we investigated the effectiveness of four naturally occurring pore-forming antimicrobial peptides (melittin, magainin 2, cecropin A, and mastoparan B) against a panel of clinically relevant pathogens, including Candida albicans, Candida parapsilosis, Candida tropicalis, and Candida glabrata. We present data on the antifungal activities of the four pore-forming peptides, assessed with descriptive statistics, and their cytocompatibility with cultured human cells. Among the four peptides, mastoparan B (MB) displayed potent antifungal activity, whereas cecropin A was the least potent. We show that MB susceptibility of phylogenetically distant non-candida albicans can vary and be described by different intrinsic physicochemical parameters of pore-forming α-helical peptides. These findings have potential therapeutic implications for the design and development of safe antifungal peptide-based drugs.

Efficacy and Safety of Repeated Micropulse Transscleral Diode Cyclophotocoagulation in Advanced Glaucoma.

PRECIS: Repeat micropulse transscleral cyclophotocoagulation (MPTCP) has some benefit in lowering intraocular pressure (IOP). There was a small risk of loss of vision, prolonged hypotony, and phthisis bulbi. AIM: This study aimed to determine the efficacy and safety of repeated MPTCP for an Asian population with refractory glaucoma. METHODS: This is a retrospective case series of 43 eyes (43 patients) with severe glaucoma which underwent repeated MPTCP. Baseline parameters were taken from the visit just before the second MPTCP session. Success was defined as IOP of 6 to 21 mm Hg or ≥20% reduction in IOP without an increase in glaucoma medication from baseline, without further glaucoma reoperation, and ≤3 total MPTCP episodes. The IOP, number of IOP-lowering medications, and best-corrected visual acuity were documented preoperatively and postoperatively. Postoperative complications were also analyzed. RESULTS: The mean age±SD was 57.4±18.2 years with a mean follow-up duration of 28.9±27.5 months. Neovascular glaucoma was the most common type of glaucoma [18 eyes (41.9%)]. The success rates at postoperative years 1, 2, and 3, and the latest follow-up were 36.4%, 42.9%, 32.0%, and 39.5%, respectively. The median survival time of repeat MPTCP was 4.6 months. Compared with the preoperative mean IOP (35.2±11.0 mm Hg), the mean IOP at postoperative years 1, 2, and 3, and latest follow-up, was 27.8±13.7 mm Hg (P=0.004), 27.4±12.4 (P=0.003), 31.8±13.2 (P=0.35), and 27.1±13.8 mm Hg (P=0.002), respectively. The mean number of IOP-lowering medications was reduced from 3.3±0.9 preoperatively to 2.8±1.3 at the final follow-up (P=0.007). Postoperative complications included prolonged hypotony [3 eyes (7.0%)] and phthisis bulbi [2 eyes (4.7%)]. CONCLUSION: Repeated MPTCP is at best moderately effective in lowering IOP for eyes with advanced glaucoma.

Clinical Efficacy and Safety Outcomes of Micropulse Transscleral Diode Cyclophotocoagulation in Patients With Advanced Glaucoma.

PRECIS: Micropulse transscleral cyclophotocoagulation (MPTCP) is only moderately effective in lowering intraocular pressure (IOP) and is useful as an adjunct procedure to other glaucoma surgeries. There was a small risk of loss of vision, prolonged hypotony, and phthisis bulbi. AIM: The aim of this study was to determine the efficacy and safety of a single MPTCP treatment for an Asian population with advanced glaucoma. METHODS: This is a retrospective single-center study of 207 eyes (207 patients) with advanced glaucoma which underwent first-time MPTCP between January 1, 2008, and March 31, 2018. Success was defined as IOP of 6 to 21 mm Hg or ≥20% reduction in IOP without an increase in glaucoma medication from baseline, and without glaucoma reoperation. The IOP, best-corrected visual acuity, and number of glaucoma medications were also analyzed. RESULTS: The mean (SD) age was 64.9±16.9 years. The mean follow-up duration was 18.7±16.2 months. The rate of success at postoperative years 1 and 2 follow-up was 44.1% and 32.6%, respectively. The median survival time of MPTCP was 9.0 months and 85 (40.9%) eyes received reoperation. The mean IOP decreased from 31.5±12.0 mm Hg preoperatively to 22.1±10.3 and 23.8±11.8 mm Hg at postoperative years 1 and 2, respectively (P<0.0001). The mean number of glaucoma medications was reduced from 3.3±1.0 preoperatively to 2.6±1.1 and 2.4±1.1 at postoperative years 1 and 2, respectively (P<0.0001). Significant complications included prolonged hypotony [1 eye (0.5%)], phthisis bulbi [7 eyes (3.4%)], and best-corrected visual acuity reduction [29 eyes (13.9%)]. CONCLUSION: Single first-time MPTCP for advanced glaucoma eyes was moderately effective in lowering IOP but >50% failed by 1 year.

The relationship between fears of cancer recurrence and patient age: A systematic review and meta-analysis.

BACKGROUND: Fears of cancer recurrence (FCR) is one of the most prevalent concerns and a common unmet need reported by cancer patients. Patient age is a demographic variable that has been linked to FCR, among others. Although it is recognised by researchers that age and FCR may be negatively correlated, the strength of this correlation has yet to be established. AIM: The aims of this study were to (a) conduct a meta-analysis to investigate the overall association of patient age in years with FCR across studies from 2009 to February 2019 and (b) scrutinise for patterns of these effect sizes across studies. METHODS AND RESULTS: Peer-reviewed papers were gathered from the literature via online databases (PubMed, EMBASE, MEDLINE, and PsycINFO). Systematic review guidelines including a quality assessment were applied to the 31 selected studies (pooled participant N size = 19 777). The meta-analysis demonstrated a significant negative association between age and FCR (ES = -0.12; 95% CI, -0.17, -0.07). Meta-regression revealed the association of patient age and FCR significantly reduced over the last decade. A significant effect (ß = -0.17, P = 0.005) of breast cancer versus other cancers on this age by FCR association was also identified. CONCLUSION: The reliable and readily accessible personal information of age of patient can be utilised as a weak indicator of FCR level especially in the breast cancer field, where the majority of studies were drawn. The suggestion that age and FCR association may be attenuated in recent years requires confirmation.

Mussel-Inspired Durable Antimicrobial Contact Lenses: The Role of Covalent and Noncovalent Attachment of Antimicrobials.

Contact lens is a major risk factor for microbial keratitis among contact lens wearers. Chemical strategies that can prevent microbial adhesion and biofilm formation are required to improve a wearer's hygiene and safety. Taking advantage of the material-independent properties of a polydopamine (pDA) coating, we investigated the role of covalent/noncovalent interactions of the antimicrobials and pDA in conferring long-term antimicrobial activities. The developed antimicrobial contact lenses not only retain their antibacterial efficiency against different bacterial strains for 2 weeks but also inhibit microbial adhesion and biofilm formation on the lens surfaces. The designed antimicrobial coatings were found to be safe for ocular cell lines. Moreover, the antimicrobial coatings did not affect the functional and surface properties of coated contact lenses. This methodology can be used to protect the contact lenses from microbial contamination for prolonged periods and has the potential to be extended for designing antimicrobial coatings for other medical devices as well.

Association between Coronary Artery Measurements and Retinal Microvasculature in Children with New Onset of Kawasaki Disease.

About a quarter of children with new onset of Kawasaki disease (KD) encounter coronary arterial involvement. While KD is known to cause vasculitis of medium-sized vessels, few studies have been done to study the involvement of the microcirculation. We aimed to investigate the association between coronary arterial dilatation and retinal microvasculature in a pilot setting, in order to further study the pathophysiological mechanism of KD from the perspective of small vessels changes. We performed a cross-sectional, observational, hospital-based study on 11 children aged 2 years and above with new-onset KD. Cardiac imaging technicians performed the echocardiographic examinations and recorded right coronary artery (RCA), left coronary artery (LCA) and left anterior descending artery (LAD). Qualified retinal graders reviewed and graded standardised retinal photographs to assess retinal microvascular parameters. Among 11 participants, there were 7 boys and 4 girls. Median and interquartile range of participants' age were 5.92 (3.08) years. After adjusting for age and sex, each unit increase in LAD (mm) was significantly associated with increment of retinal arteriolar tortuosity (4.25 × 10-5 units, 95% Confidence Interval: 1.19, 7.32). Retinal arteriolar geometric changes were associated with LAD dilatation in 11 children with new onset of KD. Our pilot provided proof-of-concept that retinal imaging might be useful for detecting coronary arterial involvement in young children with KD and it needs further investigation.

Urban meadows as an alternative to short mown grassland: effects of composition and height on biodiversity.

There are increasing calls to provide greenspace in urban areas, yet the ecological quality, as well as quantity, of greenspace is important. Short mown grassland designed for recreational use is the dominant form of urban greenspace in temperate regions but requires considerable maintenance and typically provides limited habitat value for most taxa. Alternatives are increasingly proposed, but the biodiversity potential of these is not well understood. In a replicated experiment across six public urban greenspaces, we used nine different perennial meadow plantings to quantify the relative roles of floristic diversity and height of sown meadows on the richness and composition of three taxonomic groups: plants, invertebrates, and soil microbes. We found that all meadow treatments were colonized by plant species not sown in the plots, suggesting that establishing sown meadows does not preclude further locally determined grassland development if management is appropriate. Colonizing species were rarer in taller and more diverse plots, indicating competition may limit invasion rates. Urban meadow treatments contained invertebrate and microbial communities that differed from mown grassland. Invertebrate taxa responded to changes in both height and richness of meadow vegetation, but most orders were more abundant where vegetation height was longer than mown grassland. Order richness also increased in longer vegetation and Coleoptera family richness increased with plant diversity in summer. Microbial community composition seems sensitive to plant species composition at the soil surface (0-10 cm), but in deeper soils (11-20 cm) community variation was most responsive to plant height, with bacteria and fungi responding differently. In addition to improving local residents' site satisfaction, native perennial meadow plantings can produce biologically diverse grasslands that support richer and more abundant invertebrate communities, and restructured plant, invertebrate, and soil microbial communities compared with short mown grassland. Our results suggest that diversification of urban greenspace by planting urban meadows in place of some mown amenity grassland is likely to generate substantial biodiversity benefits, with a mosaic of meadow types likely to maximize such benefits.

Designed Host Defense Peptides for the Treatment of Bacterial Keratitis.

Purpose: To limit corneal damage and potential loss of vision, bacterial keratitis must be treated aggressively. Innovation in antimicrobials is required due to the need for empirical treatment and the rapid emergence of bacterial resistance. Designed host defense peptides (dHDPs) are synthetic analogues of naturally occurring HDPs, which provide defense against invading pathogens. This study investigates the use of novel dHDPs for the treatment of bacterial keratitis. Methods: The minimum inhibitory concentrations (MICs) were determined for dHDPs on both Gram-positive and -negative bacteria. The minimum biofilm eradication concentrations (MBEC) and in vitro time-kill assays were determined. The most active dHDP, RP444, was evaluated for propensity to induce drug resistance and therapeutic benefit in a murine Pseudomonas aeruginosa keratitis model. Results: Designed HDPs were bactericidal with MICs ranging from 2 to >64 µg/mL and MBEC ranging from 6 to 750 µg/mL. In time-kill assays, dHDPs were able to rapidly reduce bacterial counts upon contact with as little as 2 µg/mL. RP444 did not induce resistance after repeated exposure of P. aeruginosa to subinhibitory concentrations. RP444 demonstrated significant efficacy in a murine model of bacterial keratitis as evidenced by a significant dose-dependent decrease in ocular clinical scores, a significantly reduced bacterial load, and substantially decreased inflammatory cell infiltrates. Conclusions: Innovative dHDPs demonstrated potent antimicrobial activity, possess a limited potential for development of resistance, and reduced the severity of murine P. aeruginosa keratitis. These studies demonstrate that a novel dHDP may have potential to treat patients with sight-threatening bacterial keratitis.

NLRP3 Inflammasome Mediates Dormant Neutrophil Recruitment following Sterile Lung Injury and Protects against Subsequent Bacterial Pneumonia in Mice.

Sterile lung injury is an important clinical problem that complicates the course of severely ill patients. Interruption of blood flow, namely ischemia-reperfusion (IR), initiates a sterile inflammatory response in the lung that is believed to be maladaptive. The rationale for this study was to elucidate the molecular basis for lung IR inflammation and whether it is maladaptive or beneficial. Using a mouse model of lung IR, we demonstrate that sequential blocking of inflammasomes [specifically, NOD-, LRR-, and pyrin domain-containing 3 (NLRP3)], inflammatory caspases, and interleukin (IL)-1ß, all resulted in an attenuated inflammatory response. IL-1ß production appeared to predominantly originate in conjunction with alveolar type 2 epithelial cells. Lung IR injury recruited unactivated or dormant neutrophils producing less reactive oxygen species thereby challenging the notion that recruited neutrophils are terminally activated. However, lung IR inflammation was able to limit or reduce the bacterial burden from subsequent experimentally induced pneumonia. Notably, inflammasome-deficient mice were unable to alter this bacterial burden following IR. Thus, we conclude that the NLRP3 inflammasome, through IL-1ß production, regulates lung IR inflammation, which includes recruitment of dormant neutrophils. The sterile IR inflammatory response appears to serve an important function in inducing resistance to subsequent bacterial pneumonia and may constitute a critical part of early host responses to infection in trauma.

Coupled electron and proton transfer processes in 4-dimethylamino-2-hydroxy-benzaldehyde.

TDDFT calculations, picosecond transient absorption, and time-resolved fluorescence studies of 4-dimethylamino-2-hydroxy-benzaldehyde (DMAHBA) have been carried out to study the electron and proton transfer processes in polar (acetonitrile) and nonpolar (n-hexane) solvents. In n-hexane, the transient absorption (TA) as well as the fluorescence originate from the ππ* state of the keto form (with the carbonyl group in the benzaldehyde ring), which is produced by an intramolecular proton transfer from the initially excited ππ* state of the enol form (OH group in the ring). The decay rate of TA and fluorescence are essentially identical in n-hexane. In acetonitrile, on the other hand, the TA exhibits features that can be assigned to the highly polar twisted intramolecular charge transfer (TICT) states of enol forms, as evidenced by the similarity of the absorption to the TICT-state absorption spectra of the closely related 4-dimethylaminobenzaldehyde (DMABA). As expected, the decay rate of the TICT-state of DMAHBA is different from the fluorescence lifetime of the ππ* state of the keto form. The occurrence of the proton and electron transfers in acetonitrile is in good agreement with the predictions of the TDDFT calculations. The very short-lived (∼1 ps) fluorescence from the ππ* state of the enol form has been observed at about 380 nm in n-hexane and at about 400 nm in acetonitrile.

Intramolecular charge transfer and dual fluorescence of 4-(dimethylamino)benzonitrile: ultrafast branching followed by a two-fold decay mechanism.

In this contribution we present new experimental and theoretical results for the intramolecular charge transfer (ICT) reaction underlying the dual fluorescence of 4-(dimethylamino)benzonitrile (DMABN), which indicate that the fully twisted ICT (TICT) state is responsible for the time-resolved transient absorption spectrum while a distinct partially twisted ICT (pTICT) structure is suggested for the fluorescent ICT state.

Photochrome that was not: 2-hydroxynaphtylidene-(8-aminoquinoline).

We report the results of quantum-chemical calculations, which show that the keto form of 2-hydroxynaphtylidene-(8-aminoquinoline) (HNAQ) is slightly more stable than the enol form both in the ground and first excited ππ* electronic states. The barrier for proton transfer between the enol and the ketone in the ground state is ca. 3300 cm(-1) (HF), and 770 cm(-1) (B3LYP), indicating a very fast (ps scale) exchange of protons between the two tautomeric forms. This barrier decreases slightly in the first excited ππ* electronic state (2500 cm(-1) - CIS), making proton exchange even faster. We show that the ππ* state of the ketone tautomer is prone to radiationless transition to a state with nearly perpendicular orientation of the two ring systems, similarly to other Schiff bases that are photochromes (for instance salicydeneaniline). This state arises when an electron from the highest occupied molecular orbital (HOMO) of the ketone ring system is transferred to a LUMO localized on the CHNH group of the bridge connecting the two ring systems of the molecule. The energy minimum of this "perpendicular" state lies only ca. 0.09 eV from the ground state potential-energy surface, thus it is prone to extremely rapid radiationless decay. Further relaxation on this surface leads to a metastable conformation that lies ca. 4440 cm(-1) above the planar, hydrogen-bonded, ketone conformation. Unfortunately, photochromism of this metastable conformation does not occur, since its absorption spectrum overlaps the spectrum of the stable species (with the predicted absorption around 438 nm vs calculated 440.6 nm in the stable ketone).

The role of the πσ* state in intramolecular charge transfer of 4-(dimethylamino)benzonitrile.

The solvent-polarity dependence and temporal characteristics of the transient absorption of 4-(dimethylamino)benzonitrile, DMABN, and 4-(dimethylamino)benzethyne, DMABE, demonstrate the presence of the πσ*-state absorption at about 700 nm and the ππ* (LE)-state absorption at about 520 nm and 450 nm. The rise and decay times of the πσ*-state transient differ from those of the ππ*-state transients in both compounds. Moreover, the peak position of the πσ*-state absorption is blue-shifted and more intense in acetonitrile as compared to n-hexane, whereas the band positions of the ππ*-state absorptions are essentially the same in the two solvents. For DMABN in acetonitrile, the rise time (∼4.3 ps) of the twisted intramolecular charge transfer (TICT)-state transient at 330 nm is identical to the decay time of the πσ*-state transient. The 4.8 ns decay time of the TICT-state absorption of DMABN is longer than the 2.9 ns decay time of the intramolecular charge-transfer (ICT) fluorescence, indicating that the fluorescent ICT state differs from the TICT state observed in transient absorption. These results are consistent with the presence of a low-lying πσ* state in DMABN (and DMABE), and the role the πσ* state plays in the formation of the TICT state of DMABN.

In vivo sodium concentration continuously monitored with fluorescent sensors.

Sodium balance is vital to maintaining normal physiological function. Imbalances can occur in a variety of diseases, during certain surgical operations or during rigorous exercise. There is currently no method to continuously monitor sodium concentration in patients who may be susceptible to hyponatremia. Our approach was to design sodium specific fluorescent sensors capable of measuring physiological fluctuations in sodium concentration. The sensors are submicron plasticized polymer particles containing sodium recognition components that are coated with biocompatible poly(ethylene) glycol. Here, the sensors were brought up in saline and placed in the subcutaneous area of the skin of mice by simple injection. The fluorescence was monitored in real time using a whole animal imager to track changes in sodium concentrations. This technology could be used to monitor certain disease states or warn against dangerously low levels of sodium during exercise.

Combined experimental and computational study of intramolecular charge transfer in p-N,N-dimethylamino-p'-cyano-diphenylacetylene.

A concerted experi-mental (time-resolved spectroscopies) and computational (TDDFT) study of p-N,N-dimethylamino-p'-cyano-diphenylacetylene (DACN-DPA) has been carried out to probe the intramolecular charge transfer (ICT) reaction that occurs in polar solvents. The picosecond transient absorption, as well as fluorescence, in acetonitrile reveals the formation of a twisted ICT(σ*) state, which involves transfer of an electron from the 4-(dimethylamino)benzethyne moiety (DMAB) to the benzonitrile (BN) group. This ICT(σ*) state, with a large dipole moment (24.7 D) and a geometry in which the plane of electron-accepting BN group is perpendicular to the plane electron-donating DMAB moiety and the angles of C(DMAB)C≡C is 135.0°, is responsible for the greatly Stokes-shifted (∼8000 cm(-1)) fluorescence and the transient absorption bands (with peaks at about 630 and 425 nm), which decays with the same lifetime (∼780 ps). It is proposed that the 630 nm picosecond transient absorption of the ICT state represents the absorption spectrum of dimethylaminobenzethyne radical cation and the 425 nm transient represents the absorption spectrum of benzonitrile radical anion. In nonpolar n-hexane, most of the fluorescence as well as the major component of the transient absorption originate from the S(1) (ππ*) state.

Role of the pisigma* state in molecular photophysics.

Photosynthesis, which depends on light-driven energy and electron transfer in assemblies of porphyrins, chlorophylls, and carotenoids, is just one example of the many complex natural systems of photobiology. A fuller understanding of the spectroscopy and photophysics of simple aromatic molecules is central to elucidating photochemical processes in the more sophisticated assemblies of photobiology. Moreover, developing a better grasp of the photophysics of simple aromatic molecules will also enhance our ability to create and improve practical applications in photochemical energy conversion, molecular nanophotonics, and molecular electronics. In this Account, we present a concerted experimental and theoretical study of aromatic ethynes, aromatic nitriles, and fluorinated benzenes, illustrating the important roles that the low-lying pisigma* state plays in the electronic relaxation of these aromatic compounds. Diphenylacetylene, 4-dialkylaminobenzonitriles, 4-dialkylaminobenzethynes, and fluorinated benzenes exhibit fluorescence that strongly quenches as the excitation energy is increased for gas-phase systems and at elevated temperatures in solution. Much of this interesting photophysical behavior can be attributed to the presence of a dark intermediate state that crosses the fluorescent pipi* state. Our quantum chemistry calculations, as well as time-resolved laser spectroscopies, indicate that this dark intermediate state is the pisigma* state that arises from the promotion of an electron from the pi orbital of the phenyl ring to the sigma* orbital localized in the C[triple bond]X group (where X is CH and N) or on the C-X group (where X is a halogen). These crossings not only lead to the strong excitation energy and temperature dependence of fluorescence but also induce highly interesting pisigma*-mediated intramolecular charge transfer in 4-dialkylaminobenzonitriles. Most previous studies on the excited-state dynamics of organic molecules have examined aromatic hydrocarbons, nitrogen heterocycles, aromatic carbonyl compounds, and polyenes, which have low-lying excited states of pipi* character (hydrocarbons and polyenes) or npi* and pipi* character (carbonyls and N-heterocycles). These studies have revealed important involvement of selection rules (promoting vibrational modes and spin-orbit coupling) and Franck-Condon factors for radiationless transitions, which have important effects on photophysical properties. The recent experimental and time-dependent density functional theory (TDDFT) calculations of aromatic ethynes, nitriles, and perfluorinated benzenes described in this Account demonstrate the importance of the bound excited state of a pisigma* configuration in these molecules.

Do fluorescence and transient absorption probe the same intramolecular charge transfer state of 4-(dimethylamino)benzonitrile?

We present here the results of time-resolved absorption and emission experiments for 4-(dimethylamino)benzonitrile in solution, which suggest that the fluorescent intramolecular charge transfer (ICT) state may differ from the twisted ICT (TICT) state observed in transient absorption.

Photophysical and spectroscopic manifestations of the low-lying pisigma* state of 4-(dimethylamino)benzethyne: solvent-polarity dependence of fluorescence and excited-state absorptions.

A concerted experimental and computational study of 4-(dimethylamino)benzethyne, DMABE, has been carried out to probe the low-lying pisigma* state and the role it plays in the photophysics of the molecule. The subpicosecond transient absorption spectra reveal the presence of a strong excited-state absorption at about 700 nm and a weaker absorption at about 520 nm. The observed absorption maxima are in excellent agreement with the TDDFT calculations that place a strongly allowed pisigma* <--pisigma* transition at 750 nm, and a weaker pipi* <--pipi* (LE) transition at 528 nm. This agreement combined with the differing decay times, and differing solvent shifts of the two transients, allow assignments of the 700 nm absorption to the pisigma* state and the 520 nm absorption to the LE (pipi*) state. The bifurcation of the initially excited L(a) (pipi*) state into the pisigma* state and the LE state, as probed by transient absorption, is strongly influenced by solvent polarity, with polar environments favoring the L(a)-->pisigma* decay channel over the competing L(a)--> LE decay channel. The nanosecond radiationless decay of the LE state to the dark pisigma* state is also strongly enhanced in polar environments, thus accounting for the dramatic quenching of fluorescence in solvents of high polarity.

Comment on "A direct approach to study radiative emission from triplet excitations in molecular semiconductors and conjugated polymers" [J. Chem. Phys. 129, 041103 (2008)].

Comparison of the experimental radiative lifetimes of the lowest triplet (T(1)) state of aromatic hydrocarbons with the lifetimes calculated using spin-orbit interaction and time-dependent spin-orbit-photon interaction operators indicates that the traditional approach, based on spin-orbit interaction, yields much better agreement with experiment.